Self-assembly of lipids (a), proteins (b), and (c) SDS-cyclodextrin complexes. SDS is a surfactant with a hydrocarbon tail (yellow) and a SO4 head (blue and red), while cyclodextrin is a saccharide ring (green C and red O atoms).Transmission electron microscopy image of an iron oxide nanoparticle. Regularly arranged dots within the dashed border are columns of Fe atoms. Left inset is the corresponding electron diffraction pattern. Scale bar: 10 nm.Iron oxide nanoparticles can be dispersed in an organic solvent (toluene). Upon its evaporation, they may self-assemble (left and right panels) into micron-sized mesocrystals
(center) or multilayers (right). Each dot in the left image is a
traditional "atomic" crystal shown in the image above. Scale bars: 100
nm (left), 25 μm (center), 50 nm (right).
STM image of self-assembled Br4-pyrene molecules on Au(111) surface (top) and its model (bottom; pink spheres are Br atoms).
Self-assembly is a process in which a disordered system of
pre-existing components forms an organized structure or pattern as a
consequence of specific, local interactions among the components
themselves, without external direction. When the constitutive components
are molecules, the process is termed molecular self-assembly.
AFM imaging of self-assembly of 2-aminoterephthalic acid molecules on (104)-oriented calcite.
Self-assembly can be classified as either static or dynamic. In static self-assembly, the ordered state forms as a system approaches equilibrium, reducing its free energy. However, in dynamic
self-assembly, patterns of pre-existing components organized by
specific local interactions are not commonly described as
"self-assembled" by scientists in the associated disciplines. These
structures are better described as "self-organized", although these terms are often used interchangeably.
Self-assembly in the classic sense can be defined as the spontaneous and reversible organization of molecular units into ordered structures by non-covalent interactions. The first property of a self-assembled system that this definition suggests is the spontaneity
of the self-assembly process: the interactions responsible for the
formation of the self-assembled system act on a strictly local level—in
other words, the nanostructure builds itself.
Although self-assembly typically occurs between
weakly-interacting species, this organization may be transferred into
strongly-bound covalent systems. An example for this may be observed in the self-assembly of polyoxometalates. Evidence suggests that such molecules assemble via a dense-phase type mechanism whereby small oxometalate ions first assemble non-covalently in solution, followed by a condensation reaction that covalently binds the assembled units. This process can be aided by the introduction of templating agents to control the formed species. In such a way, highly organized covalent molecules may be formed in a specific manner.
Self-assembled nano-structure is an object that appears as a
result of ordering and aggregation of individual nano-scale objects
guided by some physical principle.
A particularly counter-intuitive example of a physical principle that can drive self-assembly is entropy maximization. Though entropy is conventionally associated with disorder, under suitable conditions entropy can drive nano-scale objects to self-assemble into target structures in a controllable way.
Another important class of self-assembly is field-directed
assembly. An example of this is the phenomenon of electrostatic
trapping. In this case an electric field
is applied between two metallic nano-electrodes. The particles present
in the environment are polarized by the applied electric field. Because
of dipole interaction with the electric field gradient the particles are
attracted to the gap between the electrodes. Generalizations of this type approach involving different types of
fields, e.g., using magnetic fields, using capillary interactions for
particles trapped at interfaces, elastic interactions for particles
suspended in liquid crystals have also been reported.
Regardless of the mechanism driving self-assembly, people take
self-assembly approaches to materials synthesis to avoid the problem of
having to construct materials one building block at a time. Avoiding
one-at-a-time approaches is important because the amount of time
required to place building blocks into a target structure is
prohibitively difficult for structures that have macroscopic size.
Once materials of macroscopic size can be self-assembled, those
materials can find use in many applications. For example,
nano-structures such as nano-vacuum gaps are used for storing energy and nuclear energy conversion. Self-assembled tunable materials are promising candidates for large surface area electrodes in batteries and organic photovoltaic cells, as well as for microfluidic sensors and filters.
Distinctive features
At this point, one may argue that any chemical reaction driving atoms and molecules to assemble into larger structures, such as precipitation,
could fall into the category of self-assembly. However, there are at
least three distinctive features that make self-assembly a distinct
concept.
Order
First, the self-assembled structure must have a higher order
than the isolated components, be it a shape or a particular task that
the self-assembled entity may perform. This is generally not true in chemical reactions, where an ordered state may proceed towards a disordered state depending on thermodynamic parameters.
Interactions
The second important aspect of self-assembly is the predominant role of weak interactions (e.g. Van der Waals, capillary, , hydrogen bonds, or entropic forces) compared to more "traditional" covalent, ionic, or metallic bonds. These weak interactions are important in materials synthesis for two reasons.
First, weak interactions take a prominent place in materials,
especially in biological systems. For instance, they determine the
physical properties of liquids, the solubility of solids, and the organization of molecules in biological membranes.
Second, in addition to the strength of the interactions,
interactions with varying degrees of specificity can control
self-assembly. Self-assembly that is mediated by DNA pairing
interactions constitutes the interactions of the highest specificity
that have been used to drive self-assembly. At the other extreme, the least specific interactions are possibly those provided by
emergent forces that arise from entropy maximization.
Building blocks
The
third distinctive feature of self-assembly is that the building blocks
are not only atoms and molecules, but span a wide range of nano- and mesoscopic structures, with different chemical compositions, functionalities, and shapes. Research into possible three-dimensional shapes of self-assembling micrites examines Platonic solids (regular polyhedral). The term 'micrite' was created by DARPA to refer to sub-millimeter sized microrobots, whose self-organizing abilities may be compared with those of slime mold. Recent examples of novel building blocks include polyhedra and patchy particles. Examples also included microparticles with complex geometries, such as hemispherical, dimer, discs, rods, molecules, as well as multimers. These nanoscale building blocks
can in turn be synthesized through conventional chemical routes or by
other self-assembly strategies such as directional entropic forces.
More recently, inverse design approaches have appeared where it is
possible to fix a target self-assembled behavior, and determine an
appropriate building block that will realize that behavior.
Thermodynamics and kinetics
Self-assembly
in microscopic systems usually starts from diffusion, followed by the
nucleation of seeds, subsequent growth of the seeds, and ends at Ostwald ripening. The thermodynamic driving free energy can be either enthalpic or entropic or both. In either the enthalpic or entropic case, self-assembly proceeds through the formation and breaking of bonds, possibly with non-traditional forms of mediation.
The kinetics of the self-assembly process is usually related to diffusion, for which the absorption/adsorption rate often follows a Langmuir adsorption model which in the diffusion controlled concentration (relatively diluted solution) can be estimated by the Fick's laws of diffusion. The desorption rate is determined by the bond strength of the surface molecules/atoms with a thermal activation energy barrier. The growth rate is the competition between these two processes.
Examples
Important examples of self-assembly in materials science include the formation of molecular crystals, colloids, lipid bilayers, phase-separated polymers, and self-assembled monolayers.The folding of polypeptide chains into proteins and the folding of
nucleic acids into their functional forms are examples of self-assembled
biological structures. Recently, the three-dimensional macroporous
structure was prepared via self-assembly of diphenylalanine derivative
under cryoconditions, the obtained material can find the application in
the field of regenerative medicine or drug delivery system. P. Chen et al. demonstrated a microscale self-assembly method using the air-liquid interface established by Faraday wave
as a template. This self-assembly method can be used for generation of
diverse sets of symmetrical and periodic patterns from microscale
materials such as hydrogels, cells, and cell spheroids. Yasuga et al. demonstrated how fluid interfacial energy drives the
emergence of three-dimensional periodic structures in micropillar
scaffolds. Myllymäki et al. demonstrated the formation of micelles, that undergo a
change in morphology to fibers and eventually to spheres, all
controlled by solvent change.
Properties
Self-assembly extends the scope of chemistry aiming at synthesizing
products with order and functionality properties, extending chemical
bonds to weak interactions and encompassing the self-assembly of
nanoscale building blocks at all length scales. In covalent synthesis and polymerization, the scientist links atoms
together in any desired conformation, which does not necessarily have to
be the energetically most favoured position; self-assembling molecules,
on the other hand, adopt a structure at the thermodynamic minimum,
finding the best combination of interactions between subunits but not
forming covalent bonds between them. In self-assembling structures, the
scientist must predict this minimum, not merely place the atoms in the
location desired.
Another characteristic common to nearly all self-assembled systems is their thermodynamic stability. For self-assembly to take place without intervention of external forces, the process must lead to a lower Gibbs free energy,
thus self-assembled structures are thermodynamically more stable than
the single, unassembled components. A direct consequence is the general
tendency of self-assembled structures to be relatively free of defects.
An example is the formation of two-dimensional superlattices composed of an orderly arrangement of micrometre-sized polymethylmethacrylate
(PMMA) spheres, starting from a solution containing the microspheres,
in which the solvent is allowed to evaporate slowly in suitable
conditions. In this case, the driving force is capillary interaction,
which originates from the deformation of the surface of a liquid caused
by the presence of floating or submerged particles.
These two properties—weak interactions and thermodynamic
stability—can be recalled to rationalise another property often found in
self-assembled systems: the sensitivity to perturbations exerted
by the external environment. These are small fluctuations that alter
thermodynamic variables that might lead to marked changes in the
structure and even compromise it, either during or after self-assembly.
The weak nature of interactions is responsible for the flexibility of
the architecture and allows for rearrangements of the structure in the
direction determined by thermodynamics. If fluctuations bring the
thermodynamic variables back to the starting condition, the structure is
likely to go back to its initial configuration. This leads us to
identify one more property of self-assembly, which is generally not
observed in materials synthesized by other techniques: reversibility.
Self-assembly is a process which is easily influenced by external
parameters. This feature can make synthesis rather complex because of
the need to control many free parameters. Yet self-assembly has the
advantage that a large variety of shapes and functions on many length
scales can be obtained.
The fundamental condition needed for nanoscale building blocks to
self-assemble into an ordered structure is the simultaneous presence of
long-range repulsive and short-range attractive forces.
By choosing precursors
with suitable physicochemical properties, it is possible to exert a
fine control on the formation processes that produce complex structures.
Clearly, the most important tool when it comes to designing a synthesis
strategy for a material, is the knowledge of the chemistry of the
building units. For example, it was demonstrated that it was possible to
use diblock copolymers with different block reactivities in order to selectively embed maghemite nanoparticles and generate periodic materials with potential use as waveguides.
In 2008 it was proposed that every self-assembly process presents
a co-assembly, which makes the former term a misnomer. This thesis is
built on the concept of mutual ordering of the self-assembling system
and its environment.
At the macroscopic scale
The
most common examples of self-assembly at the macroscopic scale can be
seen at interfaces between gases and liquids, where molecules can be
confined at the nanoscale in the vertical direction and spread over long
distances laterally. Examples of self-assembly at gas-liquid interfaces
include breath-figures, self-assembled monolayers, droplet clusters, and Langmuir–Blodgett films, while crystallization of fullerene whiskers is an example of macroscopic self-assembly in between two liquids. Another remarkable example of macroscopic self-assembly is the formation of thin quasicrystals at an air-liquid interface, which can be built up not only by inorganic, but also by organic molecular units. Furthermore, it was reported that Fmoc protected L-DOPA amino acid (Fmoc-DOPA) can present a minimal supramolecular polymer model, displaying a
spontaneous structural transition from meta-stable spheres to fibrillar
assemblies to gel-like material and finally to single crystals.
Self-assembly processes can also be observed in systems of
macroscopic building blocks. These building blocks can be externally
propelled or self-propelled. Since the 1950s, scientists have built self-assembly systems exhibiting
centimeter-sized components ranging from passive mechanical parts to
mobile robots. For systems at this scale, the component design can be precisely
controlled. For some systems, the components' interaction preferences
are programmable. The self-assembly processes can be easily monitored
and analyzed by the components themselves or by external observers.
In April 2014, a 3D printed plastic was combined with a "smart material" that self-assembles in water, resulting in "4D printing".
Consistent concepts of self-organization and self-assembly
People regularly use the terms "self-organization" and "self-assembly" interchangeably. As complex system
science becomes more popular though, there is a higher need to clearly
distinguish the differences between the two mechanisms to understand
their significance in physical and biological systems. Both processes
explain how collective order develops from "dynamic small-scale
interactions". Self-organization is a non-equilibrium process where self-assembly is a
spontaneous process that leads toward equilibrium. Self-assembly
requires components to remain essentially unchanged throughout the
process. Besides the thermodynamic difference between the two, there is
also a difference in formation. The first difference is what "encodes
the global order of the whole" in self-assembly whereas in
self-organization this initial encoding is not necessary. Another
slight contrast refers to the minimum number of units needed to make an
order. Self-organization appears to have a minimum number of units
whereas self-assembly does not. The concepts may have particular
application in connection with natural selection. Eventually, these patterns may form one theory of pattern formation in nature.
Wave–particle duality is the concept in quantum mechanics that fundamental entities of the universe, like photons and electrons, exhibit particle or wave properties according to the experimental circumstances. It expresses the inability of the classical concepts such as particle or wave to fully describe the behavior of quantum objects. During the 19th and early 20th centuries, light
was found to behave as a wave, then later was discovered to have a
particle-like behavior, whereas electrons behaved like particles in
early experiments, then later were discovered to have wave-like
behavior. The concept of duality arose to name these seeming
contradictions.
History
Wave–particle duality of light
In the late 17th century, Sir Isaac Newton had advocated that light was corpuscular (particulate), but Christiaan Huygens
took an opposing wave description. While Newton had favored a particle
approach, he was the first to attempt to reconcile both wave and
particle theories of light, and the only one in his time to consider
both, thereby anticipating modern wave–particle duality. Thomas Young's interference experiments in 1801, and François Arago's detection of the Poisson spot in 1819, validated Huygens' wave models. However, the wave model was challenged in 1901 by Planck's law for black-body radiation. Max Planck heuristically derived a formula for the observed spectrum by assuming that a hypothetical electrically charged oscillator in a cavity that contained black-body radiation could only change its energy in a minimal increment, E, that was proportional to the frequency of its associated electromagnetic wave. In 1905 Albert Einstein interpreted the photoelectric effect also with discrete energies for photons. These both indicate particle behavior. Despite confirmation by various experimental observations, the photon theory (as it came to be called) remained controversial until Arthur Compton performed a series of experiments from 1922 to 1924 demonstrating the momentum of light.
The experimental evidence of particle-like momentum and energy
seemingly contradicted the earlier work demonstrating wave-like
interference of light.
The contradictory evidence from electrons arrived in the opposite order. Many experiments by J. J. Thomson,Robert Millikan, and Charles Wilson
among others had shown that free electrons had particle properties,
for instance, the measurement of their mass by Thomson in 1897. In 1924, Louis de Broglie introduced his theory of electron waves in his PhD thesis Recherches sur la théorie des quanta. He suggested that an electron around a nucleus could be thought of as being a standing wave
and that electrons and all matter could be considered as waves. He
merged the idea of thinking about them as particles, and of thinking of
them as waves. He proposed that particles are bundles of waves (wave packets) that move with a group velocity and have an effective mass. Both of these depend upon the energy, which in turn connects to the wavevector and the relativistic formulation of Albert Einstein a few years before.
Following de Broglie's proposal of wave–particle duality of electrons, in 1925 to 1926, Erwin Schrödinger developed the wave equation of motion for electrons. This rapidly became part of what was called by Schrödinger undulatory mechanics, now called the Schrödinger equation and also "wave mechanics".
In 1926, Max Born
gave a talk in an Oxford meeting about using the electron diffraction
experiments to confirm the wave–particle duality of electrons. In his
talk, Born cited experimental data from Clinton Davisson
in 1923. It happened that Davisson also attended that talk. Davisson
returned to his lab in the US to switch his experimental focus to test
the wave property of electrons.
In 1927, the wave nature of electrons was empirically confirmed by two experiments. The Davisson–Germer experiment at Bell Labs measured electrons scattered from Ni metal surfaces. George Paget Thomson and Alexander Reid at Cambridge University scattered electrons through thin nickel films and observed concentric diffraction rings. Alexander Reid, who was Thomson's graduate student, performed the first experiments, but he died soon after in a motorcycle accident and is rarely mentioned. These experiments were rapidly followed by the
first non-relativistic diffraction model for electrons by Hans Bethe based upon the Schrödinger equation, which is very close to how electron diffraction is now described. Significantly, Davisson and Germer noticed that their results could not be interpreted using a Bragg's law approach as the positions were systematically different; the approach of Bethe, which includes the refraction due to the average potential, yielded
more accurate results. Davisson and Thomson were awarded the Nobel Prize
in 1937 for experimental verification of wave property of electrons by
diffraction experiments. Similar crystal diffraction experiments were carried out by Otto Stern in the 1930s using beams of helium atoms and hydrogen
molecules. These experiments further verified that wave behavior is not
limited to electrons and is a general property of matter on a
microscopic scale.
Classical waves and particles
Before
proceeding further, it is critical to introduce some definitions of
waves and particles both in a classical sense and in quantum mechanics.
Waves and particles are two very different models for physical systems,
each with an exceptionally large range of application. Classical waves
obey the wave equation; they have continuous values at many points in space that vary with time; their spatial extent can vary with time due to diffraction, and they display wave interference. Physical systems exhibiting wave behavior and described by the mathematics of wave equations include water waves, seismic waves, sound waves, radio waves, and more.
Both interference and trajectories are observed in quantum systems
Some experiments on quantum systems show wave-like interference and diffraction; some experiments show particle-like collisions.
Quantum systems obey wave equations that predict particle
probability distributions. These particles are associated with discrete
values called quanta for properties such as spin, electric charge and magnetic moment.
These particles arrive one at time, randomly, but build up a pattern.
The probability that experiments will measure particles at a point in
space is the square of a complex-number valued wave. Experiments can be designed to exhibit diffraction and interference of the probability amplitude. Thus statistically large numbers of the random particle appearances can
display wave-like properties. Similar equations govern collective
excitations called quasiparticles.
The electron double slit experiment is a textbook demonstration of wave–particle duality. A modern version of the experiment is shown schematically in the figure below.
Left
half: schematic setup for electron double-slit experiment with masking;
inset micrographs of slits and mask; Right half: results for slit 1,
slit 2 and both slits open.
Electrons from the source hit a wall with two thin slits. A mask
behind the slits can expose either one or open to expose both slits. The
results for high electron intensity are shown on the right, first for
each slit individually, then with both slits open. With either slit open
there is a smooth intensity variation due to diffraction. When both
slits are open the intensity oscillates, characteristic of wave
interference.
Having observed wave behavior, now change the experiment,
lowering the intensity of the electron source until only one or two are
detected per second, appearing as individual particles, dots in the
video. As shown in the movie clip below, the dots on the detector seem
at first to be random. After some time a pattern emerges, eventually
forming an alternating sequence of light and dark bands.
Experimental electron double slit diffraction pattern. Across the middle of the image at the top the intensity alternates from
high to low showing interference in the signal from the two slits.
Bottom: movie of the pattern build up dot by dot. Click on the thumbnail to enlarge the movie.
The experiment shows wave interference revealed a single particle at a
time—quantum mechanical electrons display both wave and particle
behavior. Similar results have been shown for atoms and even large
molecules.
While electrons were thought to be particles until their wave
properties were discovered, for photons it was the opposite. In 1887, Heinrich Hertz observed that when light with sufficient frequency hits a metallic surface, the surface emits cathode rays, what are now called electrons. In 1902, Philipp Lenard discovered that the maximum possible energy of an ejected electron is unrelated to its intensity. This observation is at odds with classical electromagnetism, which
predicts that the electron's energy should be proportional to the
intensity of the incident radiation. In 1905, Albert Einstein suggested that the energy of the light must occur a finite number of energy quanta. He postulated that electrons can receive energy from an electromagnetic
field only in discrete units (quanta or photons): an amount of energyE that was related to the frequencyf of the light by
A photon of wavelength comes in from the left, collides with a target at rest, and a new photon of wavelength emerges at an angle . The target recoils, and the photons have provided momentum to the target.
where h is the Planck constant (6.626×10−34 J⋅s). Only photons of a high enough frequency (above a certain threshold value which, when multiplied by the Planck constant, is the work function)
could knock an electron free. For example, photons of blue light had
sufficient energy to free an electron from the metal he used, but
photons of red light did not. One photon of light above the threshold
frequency could release only one electron; the higher the frequency of a
photon, the higher the kinetic energy of the emitted electron, but no
amount of light below the threshold frequency could release an electron.
Despite confirmation by various experimental observations, the photon theory (as it came to be called later) remained controversial until Arthur Compton performed a series of experiments from 1922 to 1924 demonstrating the momentum of light.
Both discrete (quantized) energies and also momentum are,
classically, particle attributes. There are many other examples where
photons display particle-type properties, for instance in solar sails, where sunlight could propel a space vehicle and laser cooling where the momentum is used to slow down (cool) atoms. These are a different aspect of wave–particle duality.
Which slit experiments
In
a "which way" experiment, particle detectors are placed at the slits to
determine which slit the electron traveled through. When these
detectors are inserted, quantum mechanics predicts that the interference
pattern disappears because the detected part of the electron wave has
changed (loss of coherence). Many similar proposals have been made and many have been converted into experiments and tried out. Every single one shows the same result: as soon as electron trajectories are detected, interference disappears.
A simple example of these "which way" experiments uses a Mach–Zehnder interferometer, a device based on lasers and mirrors sketched below.
Interferometer schematic diagram
A laser beam along the input port splits at a half-silvered mirror. Part of the beam continues straight, passes through a glass phase shifter,
then reflects downward. The other part of the beam reflects from the
first mirror then turns at another mirror. The two beams meet at a
second half-silvered beam splitter.
Each output port has a camera to record the results. The two
beams show interference characteristic of wave propagation. If the laser
intensity is turned sufficiently low, individual dots appear on the
cameras, building up the pattern as in the electron example.
The first beam-splitter mirror acts like double slits, but in the
interferometer case we can remove the second beam splitter. Then the
beam heading down ends up in output port 1: any photon particles on this
path gets counted in that port. The beam going across the top ends up
on output port 2. In either case the counts will track the photon
trajectories. However, as soon as the second beam splitter is removed
the interference pattern disappears.
A megatsunami is an extremely large wave created by a substantial and sudden displacement of material into a body of water.
Megatsunamis have different features from ordinary tsunamis. Ordinary tsunamis are caused by underwater tectonic activity (movement of the earth's plates) and therefore occur along plate boundaries and as a result of earthquakes and the subsequent rise or fall in the sea floor
that displaces a volume of water. Ordinary tsunamis exhibit shallow
waves in the deep waters of the open ocean that increase dramatically in
height upon approaching land to a maximum run-up height of around 30 metres (100 ft) in the cases of the most powerful earthquakes. By contrast, megatsunamis occur when a large amount of material suddenly falls into water or anywhere near water (such as via a landslide, meteor impact, or volcanic eruption).
They can have extremely large initial wave heights in the hundreds of
metres, far beyond the height of any ordinary tsunami. These giant wave
heights occur because the water is "splashed" upwards and outwards by
the displacement.
A megatsunami is a tsunami with an initial waveamplitude (height)
measured in many tens or hundreds of metres. The term "megatsunami" has
been defined by media and has no precise definition, although it is
commonly taken to refer to tsunamis over 100 metres (328 ft) high. A megatsunami is a separate class of event from an ordinary tsunami and is caused by different physical mechanisms.
Normal tsunamis result from displacement of the sea floor due to
movements in the Earth's crust (plate tectonics). Powerful earthquakes
may cause the sea floor to displace vertically on the order of tens of
metres, which in turn displaces the water column above and leads to the
formation of a tsunami. Ordinary tsunamis have a small wave height
offshore and generally pass unnoticed at sea, forming only a slight
swell on the order of 30 centimetres (12 in) above the normal sea
surface. In deep water it is possible that a tsunami could pass beneath a
ship without the crew of the vessel noticing. As it approaches land,
the wave height of an ordinary tsunami increases dramatically as the sea
floor slopes upward and the base of the wave pushes the water column
above it upwards. Ordinary tsunamis, even those associated with the most
powerful strike-slip earthquakes, typically do not reach heights in
excess of 30 m (100 ft).
By contrast, megatsunamis are caused by landslides and massive
earthquakes that displace large volumes of water, resulting in waves
that may exceed the height of an ordinary tsunami by tens or even
hundreds of metres. Underwater earthquakes or volcanic eruptions do not normally generate megatsunamis, but landslides next to bodies of water resulting from earthquakes or volcanic eruptions can, since they cause a much larger amount of water displacement. If the landslide or impact occurs in a limited body of water, as happened in Lituya Bay (1958) and at the Vajont Dam (1963), then the water may be unable to disperse and one or more exceedingly large waves may result.
Submarine landslides can pose a significant hazard when they
cause a tsunami. Although a variety of different types of landslides can
cause tsunami, all the resulting tsunami have similar features such as
large run-ups close to the tsunami, but quicker attenuation compared to
tsunami caused by earthquakes. An example of this was the 17 July 1998 Papua New Guinean
landslide tsunami, in which waves up to 15 metres (49 ft) high struck a
20-kilometre (12.4-mile) section of the coast, killing 2,200 people,
yet at greater distances the tsunami was not a major hazard. This is due
to the comparatively small source area of most landslide tsunami
(relative to the area affected by large earthquakes) which causes the
generation of waves with shorter wavelengths. These waves are greatly
affected by coastal amplification (which amplifies the local effect) and
radial damping (which reduces the distal effect).
The size of landslide-generated tsunamis depends both on the geological details of the landslide (such as its Froude number) and also on assumptions about the hydrodynamics
of the model used to simulate tsunami generation, thus they have a
large margin of uncertainty. Generally, landslide-induced tsunamis decay
more quickly with distance than earthquake-induced tsunamis, as the former, often having a dipole structure at the source, tend to spread out radially and have a shorter wavelength (the rate at
which a wave loses energy is inversely proportional to its wavelength,
so the longer the wavelength of a wave, the more slowly it loses energy) while the latter disperses little as it propagates away perpendicularly to the source fault. Testing whether a given tsunami model is correct is complicated by the rarity of giant collapses.
Recent findings show that the nature of a tsunami depends upon
the volume, velocity, initial acceleration, length, and thickness of the
landslide generating it. Volume and initial acceleration are the key
factors which determine whether a landslide will form a tsunami. A
sudden deceleration of the landslide may also result in larger waves.
The length of the slide influences both the wavelength and the maximum
wave height. Travel time or run-out distance of the slide also will
influence the resulting tsunami wavelength. In most cases, submarine
landslides are noticeably subcritical, that is, the Froude number
(the ratio of slide speed to wave propagation) is significantly less
than one. This suggests that the tsunami will move away from the
wave-generating slide, preventing the buildup of the wave. Failures in
shallow waters tend to produce larger tsunamis because the wave is more
critical as the speed of propagation is less. Furthermore, shallower
waters are generally closer to the coast, meaning that there is less
radial damping by the time the tsunami reaches the shore. Conversely
tsunamis triggered by earthquakes are more critical when the seabed
displacement occurs in the deep ocean, as the first wave (which is less
affected by depth) has a shorter wavelength and is enlarged when
travelling from deeper to shallower waters.
Determining a height range typical of megatsunamis is a complex
and scientifically debated topic. This complexity is increased by the
two different heights often reported for tsunamis – the height of the
wave itself in open water and the height to which it surges when it
encounters land. Depending upon the locale, this second height, the "run-up height," can be several times larger than the wave's height just before it reaches shore. While there is no minimum or average height classification for
megatsunamis that the scientific community broadly accepts, the limited
number of observed megatsunami events in recent history have all had
run-up heights that exceeded 100 metres (300 ft). The megatsunami in Spirit Lake in Washington in the United States generated by the 1980 eruption of Mount St. Helens
reached 260 metres (853 ft), while the tallest megatsunami ever
recorded (in Lituya Bay in 1958) reached a run-up height of 520 metres
(1,720 ft). It is also possible that much larger megatsunamis occurred in
prehistory; researchers analyzing the geological structures left behind
by prehistoric asteroid impacts have suggested that these events could
have resulted in megatsunamis that exceeded 1,500 metres (4,900 ft) in
height.
Before the 1950s, scientists had theorized that tsunamis orders of
magnitude larger than those observed with earthquakes could have
occurred as a result of ancient geological processes, but no concrete
evidence of the existence of these "monster waves" had yet been
gathered. Geologists searching for oil in Alaska in 1953 observed that in Lituya Bay,
mature tree growth did not extend to the shoreline as it did in many
other bays in the region. Rather, there was a band of younger trees
closer to the shore. Forestry workers, glaciologists, and geographers
call the boundary between these bands a trim line.
Trees just above the trim line showed severe scarring on their seaward
side, while those from below the trim line did not. This indicated that a
large force had impacted all of the elder trees above the trim line,
and presumably had killed off all the trees below it. Based on this
evidence, the scientists hypothesized that there had been an unusually
large wave or waves in the deep inlet. Because this is a recently
deglaciated fjord with steep slopes and crossed by a major fault (the Fairweather Fault), one possibility was that this wave was a landslide-generated tsunami.
On 9 July 1958, a 7.8 Mwstrike-slip earthquake in Southeast Alaska
caused 80,000,000 metric tons (90,000,000 short tons) of rock and ice
to drop into the deep water at the head of Lituya Bay. The block fell
almost vertically and hit the water with sufficient force to create a wave
that surged up the opposite side of the head of the bay to a height of
520 metres (1,710 feet), and was still many tens of metres high further
down the bay when it carried eyewitnesses Howard Ulrich and his son
Howard Jr. over the trees in their fishing boat. They were washed back
into the bay and both survived.
Analysis of mechanism
The
mechanism giving rise to megatsunamis was analysed for the Lituya Bay
event in a study presented at the Tsunami Society in 1999; this model was considerably developed and modified by a second study in 2010.
Although the earthquake which caused the megatsunami was
considered very energetic, it was determined that it could not have been
the sole contributor based on the measured height of the wave. Neither
water drainage from a lake, nor a landslide, nor the force of the
earthquake itself were sufficient to create a megatsunami of the size
observed, although all of these may have been contributing factors.
Instead, the megatsunami was caused by a combination of events in
quick succession. The primary event occurred in the form of a large and
sudden impulsive
impact when about 40 million cubic yards of rock several hundred metres
above the bay was fractured by the earthquake, and fell "practically as
a monolithic unit" down the almost-vertical slope and into the bay. The rockfall also caused air to be "dragged along" due to viscosity effects, which added to the volume of displacement, and further impacted the sediment on the floor of the bay, creating a large crater. The study concluded that:
The giant wave runup
of 1,720 feet (524 m) at the head of the Bay and the subsequent huge
wave along the main body of Lituya Bay which occurred on July 9, 1958,
were caused primarily by an enormous subaerial rockfall into Gilbert
Inlet at the head of Lituya Bay, triggered by dynamic earthquake ground
motions along the Fairweather Fault.
The large monolithic mass of rock struck the sediments at bottom
of Gilbert Inlet at the head of the bay with great force. The impact
created a large crater and displaced and folded recent and Tertiary
deposits and sedimentary layers to an unknown depth. The displaced water
and the displacement and folding of the sediments broke and uplifted
1,300 feet of ice along the entire front face of the Lituya Glacier at
the north end of Gilbert Inlet. Also, the impact and the sediment
displacement by the rockfall resulted in an air bubble and in water
splashing action that reached the 1,720-foot (524 m) elevation on the
other side of the head of Gilbert Inlet. The same rockfall impact, in
combination with the strong ground movements, the net vertical crustal
uplift of about 3.5 feet, and an overall tilting seaward of the entire
crustal block on which Lituya Bay was situated, generated the giant
solitary gravity wave which swept the main body of the bay.
This was the most likely scenario of the event – the "PC model" that was
adopted for subsequent mathematical modeling studies with source
dimensions and parameters provided as input. Subsequent mathematical
modeling at the Los Alamos National Laboratory (Mader, 1999, Mader &
Gittings, 2002) supported the proposed mechanism and indicated that
there was indeed sufficient volume of water and an adequately deep layer
of sediments in the Lituya Bay inlet to account for the giant wave
runup and the subsequent inundation. The modeling reproduced the
documented physical observations of runup.
A 2010 model that examined the amount of infill on the floor of the
bay, which was many times larger than that of the rockfall alone, and
also the energy and height of the waves, and the accounts given by
eyewitnesses, concluded that there had been a "dual slide" involving a
rockfall, which also triggered a release of 5 to 10 times its volume of
sediment trapped by the adjacent Lituya Glacier, as an almost immediate
and many times larger second slide, a ratio comparable with other events
where this "dual slide" effect is known to have happened.
Examples
Prehistoric
An astronomical object between 37 and 58 kilometres (23 and 36 mi) wide traveling at 20 kilometres (12.4 mi) per second struck the Earth 3.26 billion years ago east of what is now Johannesburg, South Africa, near South Africa's border with Eswatini, in what was then an Archean
ocean that covered most of the planet, creating a crater about 500
kilometres (310 mi) wide. The impact generated a megatsunami that
probably extended to a depth of thousands of meters beneath the surface
of the ocean and probably rose to the height of a skyscraper when it reached shorelines. The resultant event created the Barberton Greenstone Belt.
The asteroid linked to the extinction of dinosaurs, which created the Chicxulub crater in the Yucatán Peninsula
approximately 66 million years ago, would have caused a megatsunami
over 100 metres (330 ft) tall. The height of the tsunami was limited due
to relatively shallow sea in the area of the impact; had the asteroid
struck in the deep sea the megatsunami would have likely been 4.6
kilometres (2.9 mi) tall. Among the mechanisms triggering megatsunamis
were the direct impact, shockwaves, returning water in the crater with a
new push outward and seismic waves with a magnitude up to ~11. A more recent simulation of the global effects of the Chicxulub
megatsunami showed an initial wave height of 1.5 kilometres (0.9 mi),
with later waves up to 100 metres (330 ft) in height in the Gulf of
Mexico, and up to 14 metres (46 ft) in the North Atlantic and South
Pacific; the discovery of mega-ripples in Louisiana via seismic imaging
data, with average wavelengths of 600 metres (2,000 ft) and average wave
heights of 16 metres (52 ft), looks like to confirm it. David Shonting and Cathy Ezrailson propose an "Edgerton effect"
mechanism generating the megatsunami, similar to a milk drop falling on
water that triggers a crown-shape water column, with a comparable height
to the Chicxulub impactor's,
that means over 10–12 kilometres (6–7 mi) for the initial seawater
forced outward by the explosion and blast waves; then, its collapse
triggers megatsunamis changing their height according to the different
water depth, raising up to 500 metres (1,600 ft). Furthermore, the initial shock wave via impact triggered seismic waves producing giant landslides and slumping around the region (the largest known event deposits on Earth) with subsequent megatsunamis of various sizes, and seiches of 10 to 100 metres (30 to 300 ft) in Tanis,
3,000 kilometres (1,900 mi) away, part of a vast inland sea at the time
and directly triggered via seismic shaking by the impact within a few
minutes.
During the Messinian (ca. 7.25–ca. 5.3 million years ago) various megatsunamis likely struck the coast of northern Chile.
Reservoir-induced seismicity at the end of or shortly after the Zanclean Flood (ca. 5.33 million years ago), which rapidly filled the Mediterranean Basin with water from the Atlantic Ocean, created a megatsunami with a height of nearly 100 metres (330 ft) which struck the coast of Spain near what is now Algeciras.
The Eltanin impact
in the southeast Pacific Ocean 2.5 million years ago caused a
megatsunami that was over 200 metres (660 ft) high in southern Chile and
the Antarctic Peninsula; the wave swept across much of the Pacific
Ocean.
The northern half of the East Molokai Volcano on Molokai in Hawaii
suffered a catastrophic collapse about 1.5 million years ago,
generating a megatsunami, and now lies as a debris field scattered
northward across the ocean bottom, while what remains on the island are the highest sea cliffs in the world. The megatsunami may have reached a height of 610 metres (2,000 ft) near its origin and reached California and Mexico.
In Hawaii, a megatsunami at least 400 metres (1,312 ft) in height deposited marine sediments at a modern-day elevation of 326 metres (1,070 ft) – 375 to 425 metres (1,230 to 1,394 ft) above sea level at the time the wave struck – on Lanai about 105,000 years ago. The tsunami also deposited such sediments at an elevation of 60 to 80 metres (197 to 262 ft) on Oahu, Molokai, Maui, and the island of Hawaii.
The collapse of the ancestral Mount Amarelo on Fogo in the Cape Verde Islands about 73,000 years ago triggered a megatsunami which struck Santiago, 55 kilometres (34 mi; 30 nmi) away, with a height of 170 to 240 metres (558 to 787 ft) and a run-up
height of over 270 metres (886 ft). The wave swept 770-tonne
(760-long-ton; 850-short-ton) boulders 600 metres (2,000 ft) inland and
deposited them 200 metres (656 ft) above sea level
A major collapse of the western edge of the Lake Tahoe
basin, a landslide with a volume of 12.5 cubic kilometres (3.0 cu mi)
which formed McKinney Bay between 21,000 and 12,000 years ago, generated
megatsunamis/seiche waves
with an initial height of probably about 100 m (330 ft) and caused the
lake's water to slosh back and forth for days. Much of the water in the
megatsunamis washed over the lake's outlet at what is now Tahoe City, California, and flooded down the Truckee River, carrying house-sized boulders as far downstream as the California-Nevada border at what is now Verdi, California.
In the North Sea, the Storegga Slide caused a megatsunami approximately 8,200 years ago. It is estimated to have completely flooded the remainder of Doggerland.
Around 6370 BCE, a 25-cubic-kilometre (6 cu mi) landslide on the eastern slope of Mount Etna in Sicily into the Mediterranean Sea triggered a megatsunami in the Eastern Mediterranean with an initial wave height along the eastern coast of Sicily of 40 metres (131 ft). It struck the Neolithic village of Atlit Yam off the coast of Israel with a height of 2.5 metres (8 ft 2 in), prompting the village's abandonment.
Around 5650 B.C., a landslide in Greenland created a megatsunami with a run-up height on Alluttoq Island of 41 to 66 metres (135 to 217 ft).
Around 5350 B.C., a landslide in Greenland created a megatsunami with a run-up height on Alluttoq Island of 45 to 70 metres (148 to 230 ft).
The Thera volcano erupted, the force of the eruption causing megatsunamis which affected the whole Aegean Sea and the eastern Mediterranean Sea.
c. 1100 BC: Lake Crescent
An earthquake generated the 7,200,000-cubic-metre (9,400,000 cu yd) Sledgehammer Point Rockslide, which fell from Mount Storm King in what is now Washington in the United States and entered waters at least 140 metres (459 ft) deep in Lake Crescent, generating a megatsunami with an estimated maximum run-up height of 82 to 104 metres (269 to 341 ft).
On 17 February 1674, between 19:30 and 20:00 local time, an earthquake struck the Maluku Islands. Ambon Island received run-up
heights of 100 metres (328 ft), making the wave far too large to be
caused by the quake itself. Instead, it was probably the result of an
underwater landslide triggered by the earthquake. The quake and tsunami
killed 2,347 people.
1731: Storfjorden, Norway
At 10:00 p.m. on 8 January 1731, a landslide
with a volume of possibly 6,000,000 cubic metres (7,800,000 cu yd) fell
from the mountain Skafjell from a height of 500 metres (1,640 ft) into
the Storfjorden opposite Stranda, Norway.
The slide generated a megatsunami 30 metres (100 ft) in height that
struck Stranda, flooding the area for 100 metres (330 ft) inland and
destroying the church and all but two boathouses, as well as many boats. Damaging waves struck as far away as Ørskog. The waves killed 17 people.
An eruption of Oshima-Ōshima occurred that lasted from 18 August
1741 to 1 May 1742. On 29 August 1741, a devastating tsunami occurred. It killed at least 1,467 people along a 120-kilometre (75 mi) section
of the coast, excluding native residents whose deaths were not recorded.
Wave heights for Gankakezawa have been estimated at 34 metres (112 ft)
based on oral histories, while an estimate of 13 metres (43 ft) is
derived from written records. At Sado Island, over 350 kilometres
(217 mi; 189 nmi) away, a wave height of 2 to 5 metres (6 ft 7 in to
16 ft 5 in) has been estimated based on descriptions of the damage,
while oral records suggest a height of 8 metres (26 ft). Wave heights
have been estimated at 3 to 4 metres (9.8 to 13.1 ft) even as far away
as the Korean Peninsula. There is still no consensus in the debate as to what caused it but much
evidence points to a landslide and debris avalanche along the flank of
the volcano. An alternative hypothesis holds that an earthquake caused
the tsunami.The event reduced the elevation of the peak of Hishiyama from 850 to
722 metres (2,789 to 2,369 ft). An estimated 2.4-cubic-kilometre
(0.58 cu mi) section of the volcano collapsed onto the seafloor
north of the island; the collapse was similar in size to the
2.3-cubic-kilometre (0.55 cu mi) collapse which occurred during the 1980 eruption of Mount St. Helens.
1756: Langfjorden, Norway
Just
before 8:00 p.m. on 22 February 1756, a landslide with a volume of
12,000,000 to 15,000,000 cubic metres (16,000,000 to 20,000,000 cu yd)
travelled at high speed from a height of 400 metres (1,300 ft) on the
side of the mountain Tjellafjellet into the Langfjorden
about 1 kilometre (0.6 mi) west of Tjelle, Norway, between Tjelle and
Gramsgrø. The slide generated three megatsunamis in the Langfjorden and
the Eresfjorden
with heights of 40 to 50 metres (130 to 160 ft). The waves flooded the
shore for 200 metres (660 ft) inland in some areas, destroying farms and
other inhabited areas. Damaging waves struck as far away as Veøya, 25 kilometres (16 mi) from the landslide – where they washed inland 20 metres (66 ft) above normal flood levels – and Gjermundnes,
40 kilometres (25 mi) from the slide. The waves killed 32 people and
destroyed 168 buildings, 196 boats, large amounts of forest, and roads
and boat landings.
On 21 May 1792, a flank of the Mayamaya dome of Mount Unzen
collapsed after two large earthquakes. This had been preceded by a
series of earthquakes coming from the mountain, beginning near the end
of 1791. Initial wave heights were 100 metres (330 ft), but when they
hit the other side of Ariake Bay, they were only 10 to 20 metres (33 to
66 ft) in height, though one location received 57-metre (187 ft) waves
due to seafloortopography.
The waves bounced back to Shimabara, which, when they hit, accounted
for about half of the tsunami's victims. According to estimates, 10,000
people were killed by the tsunami, and a further 5,000 were killed by
the landslide. As of 2011, it was the deadliest known volcanic event in
Japan.
1853–1854: Lituya Bay, Alaska
Sometime between August 1853 and May 1854, a megatsunami occurred in Lituya Bay in what was then Russian America.
Studies of Lituya Bay between 1948 and 1953 first identified the event,
which probably occurred because of a large landslide on the south shore
of the bay near Mudslide Creek. The wave had a maximum run-up height of 120 metres (394 ft), flooding the coast of the bay up to 230 metres (750 ft) inland.
1874: Lituya Bay, Alaska
A study of Lituya Bay in 1953 concluded that sometime around 1874, perhaps in May 1874, another megatsunami occurred in Lituya Bay in Alaska.
Probably occurring because of a large landslide on the south shore of
the bay in the Mudslide Creek Valley, the wave had a maximum run-up height of 24 metres (80 ft), flooding the coast of the bay up to 640 metres (2,100 ft) inland.
The massive explosion of Krakatoa created pyroclastic flows which generated megatsunamis when they hit the waters of the Sunda Strait on 27 August 1883. The waves reached heights of up to 24 metres (79 feet) along the south coast of Sumatra and up to 42 metres (138 feet) along the west coast of Java. The tsunamis were powerful enough to kill over 30,000 people, and their effect was such that an area of land in Banten
had its human settlements wiped out, and they never repopulated. (This
area rewilded and was later declared a national park.) The steamshipBerouw, a colonial gunboat,
was flung over a mile (1.6 km) inland on Sumatra by the wave, killing
its entire crew. Two thirds of the island collapsed into the sea after
the event. Groups of human skeletons were found floating on pumice numerous times, up to a year after the event. The eruption also generated what is often called the loudest sound in
history, which was heard 4,800 kilometres (3,000 mi; 2,600 nmi) away on Rodrigues in the Indian Ocean.
1905: Lovatnet, Norway
On
15 January 1905, a landslide on the slope of the mountain Ramnefjellet
with a volume of 350,000 cubic metres (460,000 cu yd) fell from a height
of 500 metres (1,600 ft) into the southern end of the lake Lovatnet
in Norway, generating three megatsunamis of up to 40.5 metres (133 ft)
in height. The waves destroyed the villages of Bødal and Nesdal near the
southern end of the lake, killing 61 people – half their combined
population – and 261 farm animals and destroying 60 houses, all the
local boathouses, and 70 to 80 boats, one of which – the tourist boat Lodalen
– was thrown 300 metres (1,000 ft) inland by the last wave and wrecked.
At the northern end of the 11.7-kilometre (7.3 mi) long lake, a wave
measured at almost 6 metres (20 ft) destroyed a bridge.
1905: Disenchantment Bay, Alaska
On
4 July 1905, an overhanging glacier – since known as the Fallen Glacier
– broke loose, slid out of its valley, and fell 300 metres (1,000 ft)
down a steep slope into Disenchantment Bay in Alaska,
clearing vegetation along a path 0.8 kilometres (0.5 mi) wide. When it
entered the water, it generated a megatsunami which broke tree branches
34 metres (110 ft) above ground level 0.8 kilometres (0.5 mi) away. The
wave killed vegetation to a height of 20 metres (65 ft) at a distance of
5 kilometres (3 mi) from the landslide, and it reached heights of 15 to
35 metres (50 to 115 ft) at different locations on the coast of Haenke Island. At a distance of 24 kilometres (15 mi) from the slide, observers at Russell Fjord reported a series of large waves that caused the water level to rise and fall 5 to 6 metres (15 to 20 ft) for a half-hour.
1934: Tafjorden, Norway
On
7 April 1934, a landslide on the slope of the mountain Langhamaren with
a volume of 3,000,000 cubic metres (3,900,000 cu yd) fell from a height
of about 730 metres (2,395 ft) into the Tafjorden
in Norway, generating three megatsunamis, the last and largest of which
reached a height of between 62 and 63.5 metres (203 and 208 ft) on the
opposite shore. Large waves struck Tafjord
and Fjørå. At Tafjord, the last and largest wave was 17 metres (56 ft)
tall and struck at an estimated speed of 160 kilometres per hour
(100 mph), flooding the town for 300 metres (328 yd) inland and killing
23 people. At Fjørå, waves reached 13 metres (43 ft), destroyed
buildings, removed all soil, and killed 17 people. Damaging waves struck
as far as 50 kilometres (31 mi) away, and waves were detected at a
distance of 100 kilometres (62 mi) from the landslide. One survivor
suffered serious injuries requiring hospitalization.
1936: Lovatnet, Norway
On
13 September 1936, a landslide on the slope of the mountain
Ramnefjellet with a volume of 1,000,000 cubic metres (1,300,000 cu yd)
fell from a height of 800 metres (3,000 ft) into the southern end of the
lake Lovatnet
in Norway, generating three megatsunamis, the largest of which reached a
height of 74 metres (243 ft). The waves destroyed all farms at Bødal
and most farms at Nesdal – completely washing away 16 farms – as well as
100 houses, bridges, a power station, a workshop, a sawmill, several grain mills,
a restaurant, a schoolhouse, and all boats on the lake. A 12.6-metre
(41 ft) wave struck the southern end of the 11.7-kilometre (7.3 mi) long
lake and caused damaging flooding in the Loelva River, the lake's
northern outlet. The waves killed 74 people and severely injured 11.
1936: Lituya Bay, Alaska
On 27 October 1936, a megatsunami occurred in Lituya Bay in Alaska with a maximum run-up
height of 150 metres (490 ft) in Crillon Inlet at the head of the bay.
The four eyewitnesses to the wave in Lituya Bay itself all survived and
described it as between 30 and 76 metres (100 and 250 ft) high. The
maximum inundation distance was 610 metres (2,000 ft) inland along the
north shore of the bay. The cause of the megatsunami remains unclear,
but may have been a submarine landslide.
Damage from the 1958 Lituya Bay, Alaska earthquake and megatsunami can be seen in this oblique aerial photograph of Lituya Bay,
Alaska as the lighter areas at the shore where trees have been stripped
away. The red arrow shows the location of the landslide, and the yellow
arrow shows the location of the high point of the wave sweeping over
the headland.
On 9 July 1958, a giant landslide at the head of Lituya Bay
in Alaska, caused by an earthquake, generated a wave that washed out
trees to a maximum elevation of 520 metres (1,710 ft) at the entrance of
Gilbert Inlet. The wave surged over the headland, stripping trees and soil down to bedrock, and surged along the fjord which forms Lituya Bay, destroying two fishing boats anchored there and killing two people. This was the highest wave of any kind ever recorded. The subsequent study of this event led to the establishment of the term
"megatsunami," to distinguish it from ordinary tsunamis.
On 9 October 1963, a landslide above Vajont Dam in Italy produced a 250 m (820 ft) surge that overtopped the dam and destroyed the villages of Longarone,
Pirago, Rivalta, Villanova, and Faè, killing nearly 2,000 people. This
is currently the only known example of a megatsunami that was indirectly
caused by human activities.
On 18 May 1980, the upper 400 metres (1,300 ft) of Mount St. Helens collapsed, creating a landslide. This released the pressure on the magma trapped beneath the summit bulge which exploded as a lateral blast, which then released the pressure on the magma chamber and resulted in a plinian eruption.
One lobe of the avalanche surged onto Spirit Lake,
causing a megatsunami which pushed the lake waters in a series of
surges, which reached a maximum height of 260 metres (850 ft) above the pre-eruption water level (about 975 m (3,199 ft) ASL). Above
the upper limit of the tsunami, trees lie where they were knocked down
by the pyroclastic surge; below the limit, the fallen trees and the surge deposits were removed by the megatsunami and deposited in Spirit Lake.
2000: Paatuut, Greenland
On
21 November 2000, a landslide composed of 90,000,000 cubic metres
(120,000,000 cu yd) of rock with a mass of 260,000,000 tons fell from an
elevation of 1,000 to 1,400 metres (3,300 to 4,600 ft) at Paatuut on
the Nuussuaq Peninsula on the west coast of Greenland,
reaching a speed of 140 kilometres per hour (87 mph). About 30,000,000
cubic metres (39,000,000 cu yd) of material with a mass of 87,000,000
tons entered Sullorsuaq Strait (known in Danish as Vaigat Strait), generating a megatsunami. The wave had a run-up height of 50 metres (164 ft) near the landslide and 28 metres (92 ft) at Qullissat, the site of an abandoned settlement across the strait on Disko Island,
20 kilometres (11 nmi; 12 mi) away, where it inundated the coast as far
as 100 metres (328 ft) inland. Refracted energy from the tsunami
created a wave that destroyed boats at the closest populated village, Saqqaq, on the southwestern coast of the Nuussuaq Peninsula 40 kilometres (25 mi) from the landslide.
2007: Chehalis Lake, British Columbia, Canada
On
4 December 2007, a landslide composed of 3,000,000 cubic metres
(3,900,000 cu yd) of rock and debris fell from an elevation of 550
metres (1,804 ft) on the slope of Mount Orrock on the western short of Chehalis Lake. The landslide entered the 175-metre (574 ft) deep lake, generating a megatsunami with a run-up
height of 37.8 metres (124 ft) on the opposite shore and 6.3 metres
(21 ft) at the lake's exit point 7.5 kilometres (4.7 mi) away to the
south. The wave then continued down the Chehalis River for about 15 kilometres (9.3 mi).
2015: Taan Fiord, Alaska, US
On 9 August 2016, United States Geological Survey scientists survey run-up
damage from the 17 October 2015 megatsunami in Taan Fiord. Based on
visible damage to trees that remained standing, they estimated run-up heights in this area of 5 metres (16.4 ft).
At 8:19 p.m. Alaska Daylight Time on 17 October 2015, the side of a mountain collapsed at the head of Taan Fiord, a finger of Icy Bay in Alaska. Some of the resulting landslide came to rest on the toe of Tyndall Glacier, but about 180,000,000 short tons (161,000,000 long tons; 163,000,000
metric tons) of rock with a volume of about 50,000,000 cubic metres
(65,400,000 cu yd) fell into the fjord. The landslide generated a megatsunami with an initial height of about 100 metres (330 feet) that struck the opposite shore of the fjord, with a run-up height there of 193 metres (633 feet).
Over the next 12 minutes, the wave traveled down the fjord at a speed of up to 97 kilometres per hour (60 mph), with run-up heights of over 100 metres (328 feet) in the upper fjord to
between 30 and 100 metres (98 and 330 feet) or more in its middle
section, and 20 metres (66 feet) or more at its mouth. Still probably 12 metres (40 feet) tall when it entered Icy Bay, the tsunami inundated parts of Icy Bay's shoreline with run-ups of 4 to
5 metres (13 to 16 feet) before dissipating into insignificance at
distances of 5 kilometres (3.1 mi) from the mouth of Taan Fiord, although the wave was detected 140 kilometres (87 miles) away.
Occurring in an uninhabited area, the event was unwitnessed, and
several hours passed before the signature of the landslide was noticed
on seismographs at Columbia University in New York City.
2017: Karrat Fjord, Greenland
On
17 June 2017, 35,000,000 to 58,000,000 cubic metres (46,000,000 to
76,000,000 cu yd) of rock on the mountain Ummiammakku fell from an
elevation of roughly 1,000 metres (3,280 ft) into the waters of the Karrat Fjord.
The event was thought to be caused by melting ice that destabilised the
rock. It registered as a magnitude 4.1 earthquake and created a
100-metre (328 ft) wave. The settlement of Nuugaatsiaq, 32 kilometres (20 mi) away, saw run-up heights of 9 metres (30 ft). Eleven buildings were swept into the sea, four people died, and 170 residents of Nuugaatsiaq and Illorsuit
were evacuated because of a danger of additional landslides and waves.
The tsunami was noted at settlements as far as 100 kilometres (62 mi)
away.
2020: Elliot Creek, British Columbia, Canada
On 28 November 2020, unseasonably heavy rainfall triggered a landslide of 18,000,000 m3 (24,000,000 cu yd) into a glacial lake
at the head of Elliot Creek. The sudden displacement of water generated
a 100 m (330 ft) high megatsunami that cascaded down Elliot Creek and
the Southgate River to the head of Bute Inlet, covering a total distance of over 60 km (37 mi). The event generated a magnitude 5.0 earthquake and destroyed over 8.5 km (5.3 mi) of salmon habitat along Elliot Creek. The slope had been gradually weakened over time by the retreat of West
Grenville Glacier, causing the weight distribution in this area to
change.
On 16 September 2023 a large landslide originating 300–400 m (980–1,310 ft) above sea level entered Dickson Fjord,
triggering a tsunami exceeding 200 m (660 ft) in run-up. Run-up of 60 m
(200 ft) was observed along a 10 km (6.2 mi) stretch of coast. There
was no major damage and there were no casualties. The tsunami was
followed by a seiche that lasted for a week. The seiche produced a nine-day disturbance recorded by seismic instruments globally.
2025: Tracy Arm, Alaska
On 10 August 2025, a large landslide consisting of approximately 100,000,000 m3 (130,000,000 cu yd) of material occurred near the terminus of South Sawyer Glacier in Tracy Arm, a fjord in Southeast Alaska. A 470-to-500-metre (1,542-to-1,640-foot) run-up
occurred on the shore of Tracy Arm opposite the landslide and a run-up
of at least 30 metres (98 ft) took place at nearby Sawyer Island in
Tracy Arm. At the mouth of Tracy Arm, waves estimated at 3 to 5 metres
(10 to 15 ft) in height struck Harbour Island, where water rose at least
25 feet (7.6 m) above the high tide line. Tsunami waves of up to 36
centimetres (14 in) reached a gauge 80 miles (129 km) from the landslide
at Juneau, Alaska. According to the Alaska Earthquake Center, the event had a magnitude of Mw 5.4.
Potential future megatsunamis
In
a BBC television documentary broadcast in 2000, experts said that they
thought that a landslide on a volcanic ocean island is the most likely
future cause of a megatsunami. The size and power of a wave generated by such means could produce
devastating effects, travelling across oceans and inundating up to 25
kilometres (16 mi) inland from the coast. This research was later found
to be flawed. The documentary was produced before the experts' scientific paper was
published and before responses were given by other geologists. There
have been megatsunamis in the past, and future megatsunamis are possible but current geological consensus
is that these are only local. A megatsunami in the Canary Islands would
diminish to a normal tsunami by the time it reached the continents. Also, the current consensus for La Palma is that the region conjectured
to collapse is too small and too geologically stable to do so in the
next 10,000 years, although there is evidence for past megatsunamis
local to the Canary Islands thousands of years ago. Similar remarks
apply to the suggestion of a megatsunami in Hawaii.
British Columbia
Some geologists consider an unstable rock face at Mount Breakenridge, above the north end of the giant fresh-water fjord of Harrison Lake in the Fraser Valley of southwestern British Columbia, Canada, to be unstable enough to collapse into the lake, generating a megatsunami that might destroy the town of Harrison Hot Springs (located at its south end).
Geologists Dr. Simon Day and Dr. Steven Neal Ward consider that a megatsunami could be generated during an eruption of Cumbre Vieja on the volcanic ocean island of La Palma, in the Canary Islands, Spain. Day and Ward hypothesize that if such an eruption causes the western flank to fail, a megatsunami could be generated.
In 1949, an eruption occurred at three of the volcano's vents –
Duraznero, Hoyo Negro, and Llano del Banco. A local geologist, Juan
Bonelli-Rubio, witnessed the eruption and recorded details on various
phenomenon related to the eruption. Bonelli-Rubio visited the summit
area of the volcano and found that a fissure about 2.5 kilometres
(1.6 mi) long had opened on the east side of the summit. As a result,
the western half of the volcano – which is the volcanically active arm
of a triple-armed rift – had slipped approximately 2 metres (7 ft)
downwards and 1 metre (3 ft) westwards towards the Atlantic Ocean.
In 1971, an eruption occurred at the Teneguía vent at the southern end of the sub-aerial
section of the volcano without any movement. The section affected by
the 1949 eruption is currently stationary and does not appear to have
moved since the initial rupture.
It is likely that several eruptions would be required before failure would occur on Cumbre Vieja. The western half of the volcano has an approximate volume of 500 cubic
kilometres (120 cu mi) and an estimated mass of 1.5 trillion metric tons
(1.7×1012 short
tons). If it were to catastrophically slide into the ocean, it could
generate a wave with an initial height of about 1,000 metres (3,300 ft)
at the island, and a likely height of around 50 metres (200 ft) at the Caribbean and the Eastern North American seaboard when it runs ashore eight or more hours later. Tens of millions of lives could be lost in the cities and/or towns of St. John's, Halifax, Boston, New York, Baltimore, Washington, D.C., Miami, Havana
and the rest of the eastern coasts of the United States and Canada, as
well as many other cities on the Atlantic coast in Europe, South America
and Africa. The likelihood of this happening is a matter of vigorous debate.
Geologists and volcanologists
are in general agreement that the initial study was flawed. The current
geology does not suggest that a collapse is imminent. Indeed, it seems
to be geologically impossible right now – the region conjectured as
prone to collapse is too small and too stable to collapse within the
next 10,000 years. A closer study of deposits left in the ocean from previous landslides
suggests that a landslide would likely occur as a series of smaller
collapses rather than a single landslide. A megatsunami does seem
possible locally in the distant future as there is geological evidence
from past deposits suggesting that a megatsunami occurred with marine
material deposited 41 to 188 metres (135 to 617 ft) above sea level
between 32,000 and 1.75 million years ago. This seems to have been local to Gran Canaria.
Day and Ward have admitted that their original analysis of the danger was based on several worst case assumptions. A 2008 study examined this scenario and concluded that while it could
cause a megatsunami, it would be local to the Canary Islands and would
diminish in height, becoming a smaller tsunami by the time it reached
the continents as the waves interfered and spread across the oceans.
Hawaii
Sharp cliffs and associated ocean debris at the Kohala Volcano, Lanai and Molokai indicate that landslides from the flank of the Kilauea and Mauna Loa volcanoes in Hawaii may have triggered past megatsunamis, most recently at 120,000 BP.A tsunami event is also possible, with the tsunami potentially reaching up to about 1 kilometre (3,300 ft) in height. According to the documentary National Geographic's Ultimate Disaster: Tsunami, if a big landslide occurred at Mauna Loa or the Hilina Slump, a 30-metre (98 ft) tsunami would take only thirty minutes to reach Honolulu.
There, hundreds of thousands of people could be killed as the tsunami
could level Honolulu and travel 25 kilometres (16 mi) inland. Also, the
West Coast of America and the entire Pacific Rim could potentially be
affected.
Other research suggests that such a single large landslide is not
likely. Instead, it would collapse as a series of smaller landslides.
In 2018, shortly after the beginning of the 2018 lower Puna eruption, a National Geographic
article responded to such claims with "Will a monstrous landslide off
the side of Kilauea trigger a monster tsunami bound for California?
Short answer: No."
In the same article, geologist Mika McKinnon stated:
there are submarine landslides, and
submarine landslides do trigger tsunamis, but these are really small,
localized tsunamis. They don't produce tsunamis that move across the
ocean. In all likelihood, it wouldn't even impact the other Hawaiian
islands.
People are worried about the
catastrophic crashing of the volcano into the ocean. There's no evidence
that this will happen. It is slowly – really slowly – moving toward the
ocean, but it's been happening for a very long time.
Despite this, evidence suggests that catastrophic collapses do occur on Hawaiian volcanoes and generate local tsunamis.
Norway
Although
known earlier to the local population, a crack 2 metres (6.6 ft) wide
and 500 metres (1,640 ft) in length in the side of the mountain Åkerneset in Norway
was rediscovered in 1983 and attracted scientific attention. Located at
(62°10'52.28"N, 6°59'35.38"E), it since has widened at a rate of 4
centimetres (1.6 in) per year. Geological
analysis has revealed that a slab of rock 62 metres (203 ft) thick and
at an elevation stretching from 150 to 900 metres (492 to 2,953 ft) is
in motion. Geologists assess that an eventual catastrophic collapse of
18,000,000 to 54,000,000 cubic metres (24,000,000 to 71,000,000 cu yd)
of rock into Sunnylvsfjorden is inevitable and could generate megatsunamis of 35 to 100 metres (115 to 328 ft) in height on the fjord′s opposite shore. The waves are expected to strike Hellesylt with a height of 35 to 85 metres (115 to 279 ft), Geiranger with a height of 30 to 70 metres (98 to 230 ft), Tafjord with a height of 14 metres (46 ft), and many other communities in Norway's Sunnmøre district with a height of several metres, and to be noticeable even at Ålesund. The predicted disaster is depicted in the 2015 Norwegian film The Wave.
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