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Monday, February 10, 2020

2020 Taal Volcano eruption

From Wikipedia, the free encyclopedia
 
2020 Taal Volcano Eruption
Taal Volcano - 12 January 2020.jpg
Taal Volcano's January 12, 2020 explosion
VolcanoTaal Volcano
Start dateJanuary 12, 2020
End dateJanuary 13, 2020
(Volcanic activity still ongoing)
TypePhreatic/Strombolian
LocationBatangas, Calabarzon, Philippines
14°00′38″N 120°59′52″E
Impact3 dead, 2 missing (indirect, as of January 29, 2020) 

Taal Volcano Danger Zone.svg
Map of Batangas highlighting the areas under the 14-kilometer radius danger zone

An eruption of Taal Volcano in the Philippines began on January 12, 2020. The Philippine Institute of Volcanology and Seismology (PHIVOLCS) subsequently issued an Alert Level 4, indicating that "a hazardous explosive eruption is possible within hours to days." It was a phreatic eruption from the main crater that spewed ashes to Calabarzon, Metro Manila, some parts of Central Luzon, and Pangasinan in Ilocos Region, resulting in the suspension of classes, work schedules, and flights.

By January 26, 2020, PHIVOLCS observed inconsistent, but decreasing volcanic activity in Taal, prompting the agency to downgrade its warning to Alert Level 3.
 
 

Volcanic activity


Eruption

Phreatic explosion captured at the main crater of Taal Volcano. Video taken from the installed IP camera of PHIVOLCS monitoring Taal Volcano

The volcano erupted on the afternoon of January 12, 2020, 43 years after its previous eruption in 1977. According to PHIVOLCS director Renato Solidum, a phreatic eruption was first recorded at around 1 pm Philippine Standard Time (UTC+8). Loud rumbling sounds were also felt and heard from the volcano island. By 2:30 pm, PHIVOLCS raised the alert status to Alert Level 2 after a stronger explosion was recorded around 2 pm. It was followed by an even stronger explosion by around 3 pm that spew an ash column measuring 100 meters, prompting PHIVOLCS to upgrade the alert status to Alert Level 3 by 4 pm. Furthermore, Solidum confirmed that there was a magmatic intrusion that is likely the cause of the volcano's phreatic eruptions on Sunday morning and afternoon. PHIVOLCS ordered an evacuation in the towns of Balete, San Nicolas, and Talisay in Batangas and other towns within the shores of Taal Lake. By 7:30 pm, PHIVOLCS upgraded the alert status to Alert Level 4 after volcanic activities intensified as "continuous eruption generated a tall 10 to 15 kilometres (6.2 to 9.3 mi) steam-laden tephra column with frequent volcanic lightning that rained wet ashfall on the general north as far as Quezon City and Caloocan." Ashfall from the volcano were also experienced in Cavite and Laguna, and reached as far as Metro Manila and Pampanga.

Explosion seen from the Tagaytay City viewdeck

On Monday, January 13, PHIVOLCS reported that the volcano emitted a strombolian type of eruption between 2:48 am to 4:28 am. A lava fountain was recorded at 3:20 am. The Department of Environment and Natural Resources presented a study that the air quality index of cities in Metro Manila had worsened; Mandaluyong had the highest amount of inhalable coarse particulate matter (PM10) with 118, followed by Las Piñas (108) and Taguig (104), all of which were "considered unhealthy for sensitive groups" with respiratory issues. Meanwhile, the cities with the least amount of PM10 were San Juan and Malabon, both with "good" amounts of 22 and 28 respectively. These were followed by "moderate/fair" amounts of PM10 in Pasig (55), Parañaque (62) and Makati (63).

By January 16, European satellites observed that the sulfuric acid which filled the main crater prior to the eruption had almost completely disappeared. On January 28, the main crater emitted 800 meters of steam according to an 8am bulletin by PHIVOLCS. It was described as “below instrumental detection” while Alert Level 3 remains raised.

Seismic activity

Copernicus Sentinel-2 image of Taal Volcano on January 23, showing magmatic activity and the ash-blanketed towns of Agoncillo and Laurel.

As of Saturday, January 25, the National Disaster Risk Reduction and Management Council (NDRRMC) and the Philippine Institute of Volcanology and Seismology (PHIVOLCS) have reported a total of 950 volcano tectonic earthquakes in the Taal area since the eruption, 176 of which were felt. The strongest were a series of Mw  4.1 magnitude earthquakes originating 6 kilometres (3.7 mi) northwest of Agoncillo, Batangas, which were recorded at least thrice: at 11:56 pm on January 12, 3:11 am on January 13, and 6:35 am later that day. As a result, an Intensity III ("weak") on the PHIVOLCS Earthquake Intensity Scale was felt in Tagaytay and an Intensity II ("slightly felt") was felt in Malabon. Between 11:39 pm on January 13 and 5:50 am the following day, PHIVOLCS reported a total of 44 earthquakes in the towns of Calaca, Laurel, Lemery, Mataasnakahoy, San Luis, Taal and Talisay in Batangas, and Alfonso in Cavite; among the strongest were a magnitude Mw   3.6 in Taal, which was felt at an Intensity III in Tagaytay, and a magnitude Mw   3.9 originating 7 kilometres (4.3 mi) northeast of Talisay at 2:05 am, measuring an Intensity IV ("moderately strong") in Tagaytay and Intensity II in Malabon and Pasay.

As a result of these constant earthquakes, numerous fissures or cracks began to appear across different barangays in the Batangas towns of Agoncillo, Lemery, San Nicolas, and Talisay, the towns within the 14-kilometer radius danger zone of Taal. A fissure also transected the road connecting Agoncillo to Laurel. On Wednesday, January 15, PHIVOLCS reported that the water in the main crater lake on Taal Volcano Island has drained; the lake measured 1.9 kilometers wide and 4 metres (13 ft) above sea level. Portions of the Pansipit River, had also drained as a result of "the ground deformation caused by an upward movement of the magma"; it is the same process that caused the series of earthquakes. PHIVOLCS have also hinted on underwater fissures in Taal Lake where the water may have drained into.

By January 27 from 5 am until January 28, only 3 volcanic earthquakes were recorded with magnitudes 1.5 to 2.2, with no felt event. As recorded by the United States Geological Survey, 92 earthquakes were detected in the past 24 hours. Four of them are low frequency events, which are "caused by cracks resonating as magma and gases move toward the surface". PHIVOLCS also noted the low frequency events and they recorded 170 volcanic earthquakes in its 8 am bulletin.

Impact and response


Local response

On January 13, the provincial board of Batangas declared the province under a state of calamity following the eruption, ordering the evacuation of residents within a radius of 14 kilometres (8.7 mi) from the volcano. The United Nations Office for the Coordination of Humanitarian Affairs issued a situation report stating that an estimated number of 459,300 people are within the 14-kilometer danger zone; charity organization Save the Children estimated that 21,000 of those are children. According to the NDRRMC situational report for January 18, a total of 16,174 families or 70,413 individuals are taking shelter in 300 evacuation centers. These evacuation centers consist of over 140 schools across Batangas, Cavite and Laguna, according to the Department of Education (DepEd). A total of 96,061 people were affected and electricity was cut in seven municipalities and cities across Batangas and Cavite. The Talisay–Tagaytay Road in Calabarzon was temporarily closed because of the evacuation of the residents. Heavy ashfall reduced visibility to near zero in some parts of the Santa Rosa–Tagaytay Road. The Department of Social Welfare and Development (DSWD) also stated that there are 5,000 family food packs and sleeping kits on the way for distribution to the evacuation centers. The DSWD and the Department of Health (DOH) handed a combined total of 4.9 million (US$96,656) worth of assistance to the affected residents in Calabarzon. On January 15, Cavite Governor Jonvic Remulla declared the province under a state of calamity.

Interior Secretary Eduardo Año directed the governors, mayors and local chief executives of Central Luzon, the National Capital Region and Southern Tagalog to convene their disaster risk reduction and management councils and instantly activate their incident management teams, network operations centers and other disaster response teams. The Department of the Interior and Local Government tasked the Philippine National Police (PNP) to deploy their disaster incident management task forces, reactionary standby forces and search and rescue units to the affected areas, while the Bureau of Fire Protection were tasked to assist the PNP and local government units in the mandatory evacuation of affected residents. Año also urged the public to donate basic necessities to the victims through the local government units. The Metropolitan Manila Development Authority, Philippine Air Force and Philippine Navy personnel have been dispatched to help the victims of the Taal volcano eruption.

President Rodrigo Duterte addresses evacuees in Batangas City, January 14, 2020
 
President Rodrigo Duerte, who was in Davao City during the eruption, ordered Executive Secretary Salvador Medialdea to suspend classes and government work in Calabarzon, Central Luzon and Metro Manila. President Duterte flew to Manila on the morning of January 13 and continued with his scheduled activities there. Duterte visited evacuees in Batangas City on January 14 and pledged to provide financial assistance worth ₱130 million ($2.6 million) to the affected residents. He approved the recommendation of Defense Secretary Delfin Lorenzana to prohibit individuals from visiting or inhabiting the Taal island, declaring it a "no man's land". While addressing evacuees in Batangas City, President Duterte also pushed for the construction of additional evacuation centers to be built "simultaneously" in disaster-prone areas during his administration. Concurrently, Vice President Leni Robredo visited the municipalities of Santa Teresita and San Jose, and the city of Santo Tomas in Batangas, where she helped distribute food packs and face masks to the affected residents. Robredo stressed the lack of medicines, toilets, toiletries and sleeping mats being provided to them, other than food and water. She also requested local officials to prepare an inventory of the damage.

Following the eruption, several members of the Philippine Senate called for more action from government institutions in assisting the victims. Joel Villanueva urged the Department of Labor and Employment to issue an advisory that would guide private firms in the affected areas on deciding whether their operations should continue, considering the health and safety of its employees. Villanueva called on employers and designated safety officers to assess the safety conditions of the workplaces.[48] Imee Marcos urged the DOH and the Barangay Health Volunteers to prioritize providing clinical audits to all evacuees for them to easily access medical health care. Francis Pangilinan urged the Department of Agriculture to provide long-term funding assistance and initiate alternative livelihood programs for the affected farmers and farmworkers. Pangilinan also urged the establishment of refuge areas for the pets of evacuees, as well as rescued stray animals from the affected areas. Nancy Binay and Risa Hontiveros called on the DOH and DSWD to include N95 masks, the prescribed mask for cases of volcanic ash, and other protective equipment in the provision of relief goods. Hontiveros also urged the DOH to provide mental health services, such as access to therapists, to victims who may have been traumatized by the disaster. On January 16, Cavite-based Senator Bong Revilla participated in the distribution of relief goods in several towns of his home province, which had been placed under a state of calamity. Some senators also proposed for additional measures to be implemented in the wake of the eruption. Senate President Tito Sotto proposed cloud seeding as a method to clear the fallen ash and debris. Officials from PHIVOLCS and PAGASA, however, rejected the proposal fearing that cloud seeding may result in acid rain or lahars. Sherwin Gatchalian urged the Philippine Congress to pass an additional budget of ₱10 billion ($196.4 million) to the nation's existing calamity budget, as at least ₱35 billion ($687.9 million) is at stake from the damages caused by the eruption.

In the Philippine House of Representatives, House Speaker Alan Peter Cayetano (Pateros–Taguig) directed Leyte 4th district representative Lucy Torres Gomez, chairperson of the House Committee on Disaster Management, to collaborate with other relevant committees, government agencies and urban planning experts in composing a short-term and long-term comprehensive rehabilitation plan for the affected areas. Cavite 4th district representative Elpidio Barzaga Jr. filed House Resolution 643, ordering the House to conduct an investigation on the lack of warning from PHIVOLCS regarding the imminent eruption. Barzaga stated that PHIVOLCS had issued an Alert Level 1 on Taal Volcano (indicating a "slight increase in volcanic activity") since March 2019, but he claimed that it failed to properly disseminate information to the public. The resolution also probes the presence of permanent settlements in the Taal island, despite the PHIVOLCS having already declared the island a "permanent danger zone". House Majority Leader Martin Romualdez (Leyte 1st district), however, defended PHIVOLCS by implying the difficulty in predicting the occurrence of volcanic eruptions. Romualdez added that the House allotted to PHIVOLCS an additional ₱221.4 million ($4.3 million) in order to reform "the country's monitoring and warning program for volcanic eruption."

Senator Grace Poe and Albay 2nd district representative Joey Salceda pushed Congress to immediately pass the Department of Disaster Resilience (DDR) Bill to create the said department, an executive department responsible for disaster response and emergency management. Poe illustrated that the DDR would place the existing NDRRMC under its organizational structure and create three new bureaus (disaster resiliency, disaster preparation and response, and knowledge management and dissemination). Salceda criticized the government's current system of disaster response mobilization that requires a "time consuming and confusing" inter-agency coordination, adding that the creation of the DDR would resolve these issues by "unifying the different functions" to ensure the efficiency of disaster relief goods and personnel.

Several provinces have contributed humanitarian aid to the affected residents. The provincial government of Pampanga has sent aid, totaling in 8,500 food packs, plus teams of medical personnel, social workers, and search and rescue personnel for deployment. In addition, city governments across Metro Manila have also contributed aid, ranging from in-kind donations, toiletries, food packs, N95 masks and others. Other local governments soon pitched help, including the provincial governments of Quirino and Bulacan, which donated food packs and medical supplies. Meanwhile, farmers and traders in the provinces of Benguet and Nueva Vizcaya donated vegetables to the Taal victims.The autonomous regional government of Bangsamoro also sent ₱2 million-worth of food and non-food items as aid.

The fan base of local pop singer Sarah Geronimo organized a charity public event at Luneta Park in Manila on January 18 where attendees participate in a flash mob of the viral "Tala" dance challenge. The proceeds for participating in the event would be forwarded to the Philippine Red Cross for donations to the eruption victims.

The University of the Philippines will open its own map data of the volcano from 2014 to 2017 through its UP Training Center for Applied Geodesy and Photogrammetry to the public to speed up the rehabilitation of the affected areas.

YouTuber The Hungry Syrian Wanderer distributed face masks and also cook meals to the victims ahead to the eruption.

Economic

View of the eruption from an airplane
 
Houses at a portion of the Taal Volcano island destroyed by ashfall.
 
Demand for N95 masks increased rapidly, with some stores inflating its prices to ₱200 ($3.95) a piece from the standard ₱25–40 ($0.49–0.79). The Department of Trade and Industry (DTI) dispatched teams to monitor and observe the movement of retail prices in the market and warned businesses against raising the prices for higher profit margins. After DTI inspection, Trade Undersecretary Ruth Castelo commented that some medical establishments were selling 'fake' N95 masks, some of which are not medical-grade, and could still let in large foreign air particulates. Due to the outcome of surprise inspections and consumer complaints, DTI has imposed notices of violation to 12 of the 17 stores that were inspected in Bambang, Manila, citing that these businesses will be charged with administrative and criminal cases for violating the Consumer Act. Manila Mayor Isko Moreno threatened to revoke the permits of medical supplies chains in the city involved in the price hike of face masks. Mercury Drug, a major pharmaceutical chain, pledged to replenish supply for the masks where prices would remain steady and that it would not hoard the supply. The Department of Health imposed price controls on health-related goods, including face masks, to protect consumers from profiteering and hoarding. The DOH mandates that the prices of N95 masks, in particular, should range between ₱45–105 ($0.89–2.07).

The Philippine Stock Exchange suspended trading following the eruption on January 13.

The Department of Agriculture (DA) reported that the damage to crops caused by the eruption are estimated to be ₱3.06 billion ($60.1 million), covering 2,722 hectares (27.22 km2) that includes 1,967 animals. Fisheries in the Taal Lake, consisting of about 6,000 fish cages to capture a total of 15,033 metric tons of fish, suffered losses of ₱1.6 billion ($31.4 million). Kapeng barako and Coffea liberica crops, major products of Batangas and Cavite, have damages worth at least ₱360.5 million ($7.08 million) for 8,240 metric tons and 748 hectares (1,850 acres) of land. Pineapple plantations in the Cavite towns of Amadeo, Silang and General Trias lost 21,079 metric tons of pineapple worth ₱527.25 million ($10.4 million). Rice crops in 308 hectares (760 acres) of fields across Calabarzon were lost, amounting to ₱5.6 million ($109,985), while 5,329 metric tons of corn placed losses at ₱88.9 million ($1.7 million). The Philippine Crop Insurance Corporation reassured around 1,200 farmers and fishermen in Batangas that they are insured of a three-year zero-interest survival and recovery loan worth ₱25,000 ($494.13) each, to be provided by the Mount Carmel Rural Bank. The DA plans to distribute materials and mechanisms for crop and livestock intervention worth ₱160 million ($3.1 million), which includes 5,000 coffea mother plants and 1,000 cocoa bean seedlings from the Bureau of Plant Industry, to 17 local government units in Batangas. The Philippine Carabao Center and National Dairy Authority delivered 1 tonne (15,000,000 gr) of corn silages and 1.5 tonnes (23,000,000 gr) of rice straws, a total of 2.5 tonnes (39,000,000 gr) of dietary fiber, to Batangas.

A brickworks in Biñan, Laguna used the ash spewed from Taal to manufacture hollow blocks and bricks. Through a combination of ash, sand, cement and discarded plastic waste, around 5,000 bricks are manufactured a day and are used to rebuild houses and other buildings that were damaged by the eruption. Biñan Mayor Arman Dimaguila formally instructed residents in the city to help gather ashes and deliver it to the local brickworks.

Smart and Globe offered free calls and internet services and charging stations for those affected. Water concessionaire Manila Water, in cooperation with Batangas Provincial Disaster Risk Reduction and Management Office, sent a convoy of 30 water tankers to various evacuation centers in Batangas. The company is also sending an initial 2,000 five-gallon units of bottled water. Meralco, the country's leading power distributor, assembled solar-powered mobile charging stations at various evacuation centers across Cavite.

PhilPost announced on January 16 that it would suspend delivery and acceptance of mail in Batangas towns near the Taal Volcano which falls within the "danger zone".

Health

The Department of Health advised the public to remain indoors and minimize outdoor activities. They also advised the public to refrain from purchasing and consuming freshwater fish from the Taal Lake, such as tilapia and Sardinella tawilis, as these may have been affected by the sulfur from the eruption.

Agriculture Secretary William Dar clarified that fruits and vegetables filled with ash, including the Coffea liberica fruits that are homegrown in Batangas and Cavite, are safely consumable upon cleansing.

Air traffic

NASA animation of the volcanic plume released by Taal from January 12–13, 2020, using data from JMA's Himawari 8 satellite. The eruption disrupted several flights to and from the Luzon island.
 
On January 12, 2020, the Manila International Airport Authority (MIAA) suspended all flights to and from all terminals of the Ninoy Aquino International Airport (NAIA) in Manila following the eruption due to the various hazardous effects of volcanic ash on flight safety. The MIAA recorded that at least 516 flights from and to NAIA were suspended, with about 80,000 passengers affected. On January 13, operations at NAIA resumed partially from 10 am onwards, although many flights still remained canceled or delayed. A number of international flights bound for NAIA were diverted to either Clark International Airport in Angeles, Mactan–Cebu International Airport, Haneda Airport in Tokyo, Hong Kong International Airport, or Antonio B. Won Pat International Airport in Guam. By January 14, 604 flights were canceled according to the NDRRMC. However, by January 15, 537 of those flights had resumed operations.

The Civil Aviation Authority of the Philippines advised the Luzon International Premiere Airport Development Corporation to suspend flights at Clark International Airport as reports indicate that ash could reach the area. On January 13, only ten flights were reported to have been canceled, while nine flights were delayed.

At the Mactan–Cebu International Airport (MCIA), only 25 domestic flights (all bound for NAIA) and one international flight were canceled, all of which were on January 14. However, the MCIA had to accommodate five international flights bound for NAIA that were diverted. The GMR–Megawide Cebu Airport Corporation (GMCAC), the operator of the MCIA, requested that all diverted flights should be accommodated on a "first-come, first-serve basis" depending on the availability of aircraft parking bays. Aside from hotel bookings, passengers of the diverted flights were given small food packs. MCIA provided passengers with free bus services for inter-airport transfers and city hotel transfers. Retail stores and food concessionaires at the airport terminals immediately restocked their supply and offered discounts for passengers, available from January 12 to 14.

Sports

Collegiate leagues, the University Athletic Association of the Philippines (UAAP) and the National Collegiate Athletic Association (NCAA) postponed games to be held in Metro Manila on January 13, 2020 due to ash fall. The junior basketball and junior football ties were to be held by the UAAP and volleyball games for the NCAA. The AFC Champions League match between Ceres–Negros and Shan United scheduled for January 14, 2020 at the Rizal Memorial Stadium in Manila was threatened to be postponed due to ash fall the day before but match officials decided that game should push through.

International response

The Philippine government, while it said that it would accept any international aid, has stated that it will not actively seek for foreign aid believing that it still has the capability to deal with the Taal volcano eruption.

The China Coast Guard donated 600 pieces of N95 masks, food packs, and other relief goods to evacuees in Batangas through the Philippine Coast Guard.

The United States Agency for International Development and its Volcano Disaster Assistance Program, through the U.S. Embassy in the Philippines, is providing thermographic cameras and remote technical support to assist the Philippine government in monitoring Taal's volcanic activity. South Korea has also pledged US$200,000 in humanitarian aid through the Philippine Red Cross. The Singapore Red Cross on their part relayed about S$67,000-worth of humanitarian aid to support the operations of their Philippine counterpart. The Emirates Red Crescent also sent a delegation to the Philippines to assist on the relief operations.

American comedian Dave Chappelle, who visited Manila during the eruption, donated ₱1 million ($19,671) to the relief efforts for the eruption victims through the Rayomar Outreach Foundation.

The European Union, through its Acute Large Emergency Response Tool (ALERT), has donated 42 million (750 thousand) in humanitarian aid which includes emergency shelter, psychosocial support services including child protection services and essential household items.

Yellowstone hotspot

From Wikipedia, the free encyclopedia
 
Yellowstone hotspot
Yellowstone Caldera.svg
Schematic of the hotspot and the Yellowstone Caldera
HotspotsSRP update2013.JPG
Past locations of the hotspot in millions of years
CountryUnited States
StateIdaho/Wyoming
RegionRocky Mountains
Coordinates44.43°N 110.67°WCoordinates: 44.43°N 110.67°W

The Yellowstone hotspot is a volcanic hotspot in the United States responsible for large scale volcanism in Idaho, Montana, Nevada, Oregon, and Wyoming as the North American tectonic plate moved over it. It formed the eastern Snake River Plain through a succession of caldera-forming eruptions. The resulting calderas include the Island Park Caldera, the Henry's Fork Caldera, and the Bruneau-Jarbidge caldera. The hotspot currently lies under the Yellowstone Caldera. The hotspot's most recent caldera-forming supereruption, known as the Lava Creek eruption, took place 640,000 years ago and created the Lava Creek Tuff, and the most recent Yellowstone Caldera. The Yellowstone hotspot is one of a few volcanic hotspots underlying the North American tectonic plate; others include the Anahim and Raton hotspots.

Snake River Plain

The eastern Snake River Plain is a topographic depression that cuts across Basin and Range Mountain structures, more or less parallel to North American plate motion. Beneath more recent basalts are rhyolite lavas and ignimbrites that erupted as the lithosphere passed over the hotspot. Younger volcanoes that erupted after passing over the hotspot covered the plain with young basalt lava flows in places, including Craters of the Moon National Monument and Preserve.

The central Snake River plain is similar to the eastern plain, but differs by having thick sections of interbedded lacustrine (lake) and fluvial (stream) sediments, including the Hagerman Fossil Beds

Nevada–Oregon calderas

Although the McDermitt volcanic field on the Nevada–Oregon border is frequently shown as the site of the initial impingement of the Yellowstone Hotspot, new geochronology and mapping demonstrates that the area affected by this mid-Miocene volcanism is significantly larger than previously appreciated. Three silicic calderas have been newly identified in northwest Nevada, west of the McDermitt volcanic field as well as the Virgin Valley Caldera. These calderas, along with the Virgin Valley Caldera and McDermitt Caldera, are interpreted to have formed during a short interval 16.5–15.5 million years ago, in the waning stage of the Steens flood basalt volcanism. The northwest Nevada calderas have diameters ranging from 15–26 km and deposited high temperature rhyolite ignimbrites over approximately 5000 km2.

The Bruneau-Jarbidge caldera erupted between ten and twelve million years ago, spreading a thick blanket of ash in the Bruneau-Jarbidge event and forming a wide caldera. Animals were suffocated and burned in pyroclastic flows within a hundred miles of the event, and died of slow suffocation and starvation much farther away, notably at Ashfall Fossil Beds, located 1000 miles downwind in northeastern Nebraska, where a foot of ash was deposited. There, two hundred fossilized rhinoceros and many other animals were preserved in two meters of volcanic ash. By its characteristic chemical fingerprint and the distinctive size and shape of its crystals and glass shards, the volcano stands out among dozens of prominent ashfall horizons laid down in the Cretaceous, Paleogene, and Neogene periods of central North America. The event responsible for this fall of volcanic ash was identified as Bruneau-Jarbidge. Prevailing westerlies deposited distal ashfall over a vast area of the Great Plains

Volcanic fields


Twin Falls and Picabo volcanic fields

The Twin Falls and Picabo volcanic fields were active about 10 million years ago. The Picabo Caldera was notable for producing the Arbon Valley Tuff 10.2 million years ago.

Heise volcanic field

The Heise volcanic field of eastern Idaho produced explosive caldera-forming eruptions which began 6.6 million years ago and lasted for more than 2 million years, sequentially producing four large-volume rhyolitic eruptions. The first three caldera-forming rhyolites — Blacktail Tuff, Walcott Tuff and Conant Creek Tuff — totaled at least 2250 km3 of erupted magma. The final, extremely voluminous, caldera-forming eruption — the Kilgore Tuff — which erupted 1800 km3 of ash, occurred 4.5 million years ago.

Yellowstone Plateau

Yellowstone sits on top of three overlapping calderas.

The Yellowstone Plateau volcanic field is composed of four adjacent calderas. West Thumb Lake is itself formed by a smaller caldera which erupted 174,000 years ago. The Henry's Fork Caldera in Idaho was formed in an eruption of more than 280 km3 (67 cu mi) 1.3 million years ago, and is the source of the Mesa Falls Tuff. The Henry's Fork Caldera is nested inside of the Island Park Caldera and the calderas share a rim on the western side. The earlier Island Park Caldera is much larger and more oval and extends well into Yellowstone Park. Although much smaller than the Island Park Caldera, the Henry's Fork Caldera is still sizeable at 18 miles (29 km) long and 23 miles (37 km) wide and its curved rim is plainly visible from many locations in the Island Park area.

Of the many calderas formed by the Yellowstone Hotspot, including the later Yellowstone Caldera, the Henry's Fork Caldera is the only one that is currently clearly visible. The Henry's Fork of the Snake River flows through the Henry's Fork Caldera and drops out at Upper and Lower Mesa Falls. The caldera is bounded by the Ashton Hill on the south, Big Bend Ridge and Bishop Mountain on the west, by Thurburn Ridge on the North and by Black Mountain and the Madison Plateau on the east. The Henry's Fork caldera is in an area called Island Park. Harriman State Park is situated in the caldera.

The Island Park Caldera is older and much larger than the Henry's Fork Caldera with approximate dimensions of 58 miles (93 km) by 40 miles (64 km). It is the source of the Huckleberry Ridge Tuff that is found from southern California to the Mississippi River near St. Louis. This supereruption occurred 2.1 million years BP and produced 2500 km3 of ash. The Island Park Caldera is sometimes referred to as the First Phase Yellowstone Caldera or the Huckleberry Ridge Caldera. The youngest of the hotspot calderas, the Yellowstone Caldera, formed 640,000 years ago and is about 34 miles (55 km) by 45 miles (72 km) wide. Non-explosive eruptions of lava and less-violent explosive eruptions have occurred in and near the Yellowstone Caldera since the last super eruption. The most recent lava flow occurred about 70,000 years ago, while the largest violent eruption excavated the West Thumb of Lake Yellowstone around 150,000 years ago. Smaller steam explosions occur as well – an explosion 13,800 years ago left a 5 kilometer diameter crater at Mary Bay on the edge of Yellowstone Lake.

Both the Heise and Yellowstone volcanic fields produced a series of caldera-forming eruptions characterised by magmas with so-called "normal" oxygen isotope signatures (with heavy oxygen-18 isotopes) and a series of predominantly post-caldera magmas with so-called "light" oxygen isotope signatures (characterised as low in heavy oxygen-18 isotopes). The final stage of volcanism at Heise was marked by "light" magma eruptions. If Heise is any indication, this could mean that the Yellowstone Caldera has entered its final stage, but the volcano might still exit with a climactic fourth caldera event analogous to the fourth and final caldera-forming eruption of Heise (the Kilgore Tuff) – which was also made up of so-called "light" magmas. The appearance of "light" magmas would seem to indicate that the uppermost portion of the continental crust has largely been consumed by the earlier caldera- forming events, exhausting the melting potential of the crust above the mantle plume. In this case Yellowstone could be expiring. It could be another 1–2 million years (as the North American Plate moves across the Yellowstone hotspot) before a new supervolcano is born to the northeast, and the Yellowstone Plateau volcanic field joins the ranks of its deceased ancestors in the Snake River Plain. (References to be added: Kathryn Watts (Nov 2007) GeoTimes "Yellowstone and Heise: Supervolcanoes that Lighten Up": Kathryn E. Watts, Ilya N. Bindeman and Axel K. Schmitt (2011) Petrology, Vol. 52, No. 5, "Large-volume Rhyolite Genesis in Caldera Complexes of the Snake River Plain: Insights from the Kilgore Tuff of the Heise Volcanic Field, Idaho, with Comparison to Yellowstone and Bruneau-Jarbidge Rhyolites" pp. 857–890).

Andean orogeny

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Andean_orogeny
 
Simplified sketch of the present-situation along most of the Andes
 
The Andean orogeny (Spanish: Orogenia andina) is an ongoing process of orogeny that began in the Early Jurassic and is responsible for the rise of the Andes mountains. The orogeny is driven by a reactivation of a long-lived subduction system along the western margin of South America. On a continental scale the Cretaceous (90 Ma) and Oligocene (30 Ma) were periods of re-arrangements in the orogeny. Locally the details of the nature of the orogeny varies depending on the segment and the geological period considered.

Overview

Subduction orogeny has been occurring in what is now western South America since the break-up of the supercontinent Rodinia in the Neoproterozoic. The Paleozoic Pampean, Famatinian and Gondwanan orogenies are the immediate precursors to the later Andean orogeny. The first phases of Andean orogeny in the Jurassic and Early Cretaceous were characterized by extensional tectonics, rifting, the development of back-arc basins and the emplacement of large batholiths. This development is presumed to have been linked to the subduction of cold oceanic lithosphere. During the mid to Late Cretaceous (ca. 90 million years ago) the Andean orogeny changed significantly in character. Warmer and younger oceanic lithosphere is believed to have started to be subducted beneath South America around this time. Such kind of subduction is held responsible not only for the intense contractional deformation that different lithologies were subject to, but also the uplift and erosion known to have occurred from the Late Cretaceous onward. Plate tectonic reorganization since the mid-Cretaceous might also have been linked to the opening of the South Atlantic Ocean. Another change related to mid-Cretaceous plate tectonic changes was the change of subduction direction of the oceanic lithosphere that went from having south-east motion to having a north-east motion at about 90 million years ago. While subduction direction changed it remained oblique (and not perpendicular) to the coast of South America, and the direction change affected several subduction zone-parallel faults including Atacama, Domeyko and Liquiñe-Ofqui.

Paleogeography of the Late Cretaceous South America. Areas subject to the Andean orogeny are shown in light grey while the stable cratons are shown as grey squares. The sedimentary formations of Los Alamitos and La Colonia that formed in the Late Cretaceous are indicated.
 
Low angle subduction or flat-slab subduction has been common during the Andean orogeny leading to crustal shortening and deformation and the suppression of arc volcanism. Flat-slab subduction has occurred at different times in various part of the Andes, with northern Colombia (6–10° N), Ecuador (0–2° S), northern Peru (3–13° S) and north-central Chile and Argentina (24–30° S) experiencing these conditions at present.

The tectonic growth of the Andes and the regional climate have evolved simultaneously and have influenced each other. The topographic barrier formed by the Andes stopped the income of humid air into the present Atacama desert. This aridity, in turn, changed the normal superficial redistribution of mass via erosion and river transport, modifying the later tectonic deformation.

In the Oligocene the Farallon Plate broke up, forming the modern Cocos and Nazca plates ushering a series of changes in the Andean orogeny. The new Nazca Plate was then directed into an orthogonal subduction with South America causing ever-since uplift in the Andes, but causing most impact in the Miocene. While the various segments of the Andes have their own uplift histories, as a whole the Andes have risen significantly in last 30 million years (Oligocene–present).

Orogeny by segment


Colombia, Ecuador and Venezuela (12° N–3° S)

Map of a north-south sea-parallel pattern of rock ages in western Colombia. This pattern is a result of the Andean orogeny.
 
Tectonic blocks of continental crust that had separated from northwestern South America in the Jurassic re-joined the continent in the Late Cretaceous by colliding obliquely with it. This episode of accretion occurred in a complex sequence. The accretion of the island arcs against northwestern South America in the Early Cretaceous led to the development of a magmatic arc caused by subduction. The Romeral Fault in Colombia forms the suture between the accreted terranes the rest of South America. Around the Cretaceous–Paleogene boundary (ca. 65 million years ago) the oceanic plateau of the Caribbean large igneous province collided with South America. The subduction of the lithosphere as the oceanic plateau approached South America led to the formation of a magmatic arc now preserved in the Cordillera Real of Ecuador and the Cordillera Central of Colombia. In the Miocene an island arc and terrane (Chocó terrane) collided against northwestern South America. This terrane forms parts of what is now Chocó Department and Western Panamá.

The Caribbean Plate collided with South America in the Early Cenozoic but shifted then its movement eastward. Dextral fault movement between the South American and Caribbean plate started 17–15 million years ago. This movement was canalized along a series of strike-slip faults, but these faults alone do not account for all deformation. The northern part of the Dolores-Guayaquil Megashear forms part of the dextral fault systems while in the south the megashear runs along the suture between the accreted tectonic blocks and the rest of South America.

Northern Peru (3–13° S)

The seaward tilting of the sedimentary strata of Salto del Fraile Formation in Peru was caused by the Andean orogeny.

Long before the Andean orogeny the northern half of Peru was subject of the accretion of terranes in the Neoproterozoic and Paleozoic. Andean orogenic deformation in northern Peru can be traced to the Albian (Early Cretaceous). This first phase of deformation —the Mochica Phase— is evidenced in the folding of Casma Group sediments near the coast.

Sedimentary basins in western Peru changed from marine to continental conditions in the Late Cretaceous as a consequence of a generalized vertical uplift. The uplift in northern Peru is thought to be associated with the contemporary accretion of the Piñón terrane in Ecuador. This stage of orogeny is called the Peruvian Phase. Besides coastal Peru the Peruvian Phase affected or caused crustal shortening along the Cordillera Oriental and the tectonic inversion of Santiago Basin in the Sub-Andean zone. The bulk of the Sub-Andean zone was however unaffected by the Peruvian Phase.

After a period without much tectonic activity in the Early Eocene the Incaic Phase of orogeny occurred in the Mid and Late Eocene. No other tectonic event in the western Peruvian Andes compare with the Incaic Phase in magnitude. Horizontal shortening during the Incaic Phase resulted in the formation of the Marañón fold and thrust belt. An unconformity cutting across the Marañón fold and thrust belt show the Incaic Phase ended no later than 33 million years ago in the earliest Oligocene.

Topographic map of the Andes by NASA. The southern and northern ends of the Andes are not shown. The Bolivian Orocline is visible as a bend in the coastline and the Andes lower half of the map.
 
In the period after the Eocene the Northern Peruvian Andes were subject to the Quechua Phase of orogeny. The Quechua Phase is divided into the sub-phases Quechua 1, Quechua 2 and Quechua 3. The Quechua 1 Phase lasted from 17 to 15 million years ago and included a reactivation of Inca Phase structures in the Cordillera Occidental. 9–8 million years ago, in the Quechua 2 Phase, the older parts of the Andes in northern Peru were thrusted to the northeast. Most of the Sub-Andean zone of northern Peru deformed 7–5 million years ago (Late Miocene) during the Quechua 3 Phase. The Sub-Andean stacked in a thrust belt.

The Miocene rise of the Andes in Peru and Ecuador led to increased orographic precipitation along its eastern parts and to the birth of the modern Amazon River. One hypothesis links these two changes by assuming that increased precipitation led to increased erosion and this erosion led to filling the Andean foreland basins beyond their capacity and that it would have been the basin over-sedimentation rather than the rise of the Andes that made drainage basins flow to the east. Previously the interior of northern South America drained to the Pacific. 

Bolivian Orocline (13–26° S)

Early Andean subduction in the Jurassic formed a volcanic arc in northern Chile known as La Negra Arc. The remnants of this arc are now exposed in the Chilean Coast Range. Several plutons were emplaced in the Chilean Coast Range in the Jurassic and Early Cretaceous including the Vicuña Mackenna Batholith. Further east at similar latitudes, in Argentina and Bolivia, the Salta rift system developed during the Late Jurassic and the Early Cretaceous.

Pisco Basin, around latitude 14° S, was subject to a marine transgression in the Oligocene and Early Miocene epochs (25–16 Ma). In contrast Moquégua Basin to the southeast and the coast to south of Pisco Basin saw no transgression during this time but a steadily rise of the land.

From the Late Miocene onward the region that would become the Altiplano rose from low elevations to more than 3,000 m.a.s.l.. It is estimated that the region rose 2000 to 3000 meters in the last ten million years. Together with this uplift several valleys incised in the western flank of the Altiplano. In the Miocene the Atacama Fault moved, uplifting the Chilean Coast Range and creating sedimentary basins east of it. At the same time the Andes around the Altiplano region broadened to exceed any other Andean segment in width. Possibly about 1000 km of lithosphere has been lost due to lithospheric shortening. During subduction the western end of the forearc region flexured downward forming a giant monocline. By contrast the region east of the Altiplano is characterized by deformation and tectonics along a complex fold and thrust belt. Over-all the region surrounding the Altiplano and Puna plateaux has been horizontally shortened since the Eocene.

The Altiplano and its largest lake as seen from Ancohuma. The uplift of the Altiplano plateau is one of the most striking features of the Andean orogeny.

In southern Bolivia lithospheric shortening has made the Andean foreland basin to move eastward relative to the continent at an average rate of ca. 12–20 mm per year during most of the Cenozoic. Along the Argentine Northwest the Andean uplift has caused Andean foreland basins to separate into several minor isolated intermontane sedimentary basins. Towards the east the piling up of crust in Bolivia and the Argentine Norwest caused a north-south forebulge known as Asunción arch to develop in Paraguay.

The uplift of the Altiplano is thought to be indebted to a combination of horizontal shortening of the crust and to increased temperatures in the mantle (thermal thinning). The bend in the Andes and the west coast of South America known as the Bolivian Orocline was enhanced by Cenozoic horizontal shortening but existed already independently of it.

Besides direct causes the particular characteristics of the Bolivian Orocline–Altiplano region are attributed to a variety of deeper causes. These causes include a local steepening of the subduction angle of Nazca Plate, increased crustal shortening and plate convergence between the Nazca and South American plates, an acceleration in the westward drift of the South American Plate, and a rise in the shear stress between the Nazca and South American plates. This increase in shear stress could in turn be related to the scarcity of sediments in the Atacama trench which is caused by the arid conditions along Atacama Desert. Capitanio et al. attributes the rise of Altiplano and the bending of the Bolivian Orocline to the varying ages of the subducted Nazca Plate with the older parts of the plate subducting at the centre of the orocline. As Andrés Tassara puts it the rigidity of the Bolivian Orocline crust is derivative of the thermal conditions. The crust of the western region (forearc) of the orocline has been cold and rigid, resisting and damming up the westward flow of warmer and weaker ductile crustal material from beneath the Altiplano. The Cenozoic orogeny at the Bolivian orocline has produced a significative anatexis of crustal rocks including metasediments and gneisses resulting in the formation of peraluminous magmas. These characteristics imply that the Cenozoic tectonics and magmatism in parts of Bolivian Andes is similar to that seen in collisional orogens. The peralumineous magmatism in Cordillera Oriental is the cause of the world-class mineralizations of the Bolivian tin belt.

Tilted strata of the Yacoraite Formation at Serranía de Hornocal in northernmost Argentina. The Andean orogeny caused the tilting of these originally horizontal strata.

The rise of the Altiplano is thought by scientist Adrian Hartley to have enhanced an already prevailing aridity or semi-aridity in Atacama Desert by casting a rain shadow over the region.

Central Chile and Argentina (26–39° S)

At the latitudes between 17 and 39° S the Late Cretaceous and Cenozoic development of the Andean orogeny is characterized by an eastward migration of the magmatic belt and the development of several foreland basins. The eastward migration of the arc is thought to be caused by subduction erosion.

At the latitudes of 32–36° S —that is Central Chile and most of Mendoza Province— the Andean orogeny proper began in the Late Cretaceous when backarc basins were inverted. Immediately east of the early Andes foreland basins developed and their flexural subsidence caused the ingression of waters from the Atlantic all the way to the front of the orogen in the Maastrichtian. The Andes at the latitudes of 32–36° S experienced a sequence of uplift in the Cenozoic that started in the west and spread to the east. Beginning about 20 million years ago in the Miocene the Principal Cordillera (east of Santiago) began an uplift that lasted until about 8 million years ago. From the Eocene to the early Miocene, sediments accumulated in the Abanico Extensional Basin, a north-south elongated basin in Chile that spanned from 29° to 38° S. Tectonic inversion from 21 to 16 million years ago made the basin to collapse and the sediments to be incorporated to the Andean cordillera. Lavas and volcanic material that are now part of Farellones Formation accumulated while the basin was being inverted and uplifted. The Miocene continental divide was about 20 km to the west of the modern water divide that makes up the Argentina–Chile border. Subsequent river incision shifted the divide to the east leaving old flattish surfaces hanging. Compression and uplift in this part of the Andes has continued into the present. The Principal Cordillera had risen to heights that allowed for the development of valley glaciers about 1 million years ago.

Before the Miocene uplift of the Principal Cordillera was over, the Frontal Cordillera to the east started a period of uplift that lasted from 12 to 5 million years ago. Further east the Precordillera was uplifted in the last 10 million years and the Sierras Pampeanas has experienced a similar uplift in the last 5 million years. The more eastern part of the Andes at these latitudes had their geometry controlled by ancient faults dating to the San Rafael orogeny of the Paleozoic. The Sierras de Córdoba (part of the Sierras Pampeanas) where the effects of the ancient Pampean orogeny can be observed, owes it modern uplift and relief to the Andean orogeny in the late Cenozoic. Similarly the San Rafael Block east of the Andes and south of Sierras Pampeanas was raised in the Miocene during the Andean orogeny. In broad terms the most active phase of orogeny in area of southern Mendoza Province and northern Neuquén Province (34–38° S) happened in the Late Miocene while arc volcanism occurred east of the Andes.

At more southern latitudes (36–39° S) various Jurassic and Cretaceous marine transgressions from the Pacific are recorded in the sediments of Neuquén Basin. In the Late Cretaceous conditions changed. A marine regression occurred and the fold and thrust belts of Malargüe (36°00 S), Chos Malal (37° S) and Agrio (38° S) started to develop in the Andes and did so in until Eocene times. This meant an advance of the orogenic deformation since the Late Cretaceous that caused the western part of Neuquén Basin to stack in the Malargüe and Agrio fold and thrust belts. In the Oligocene the western part of the fold and thrust belt was subject to a short period of extensional tectonics whose structures were inverted in the Miocene. After a period of quiescence the Agrio fold and thrust belt resumed limited activity in the Eocene and then again in the Late Miocene.

In the south of Mendoza Province the Guañacos fold and thrust belt (36.5° S) appeared and grew in the Pliocene and Pleistocene consuming the western fringes of the Neuquén Basin.

Southern Patagonian Andes (48–55° S)

Syncline next to Nordenskjöld Lake in Torres del Paine National Park. The syncline formed during the Andean orogeny.

The early development of the Andean orogeny in southernmost South America affected also the Antarctic Peninsula. In southern Patagonia at the onset of the Andean orogeny in the Jurassic, extensional tectonics created the Rocas Verdes Basin, a back-arc basin whose southeastern extension survives as the Weddell Sea in Antarctica. In the Late Cretaceous the tectonic regime of Rocas Verdes Basin changed leading to its transformation into a compressional foreland basin –the Magallanes Basin– in the Cenozoic. This change was associated with an eastward move of the basin depocenter and the obduction of ophiolites. The closure of Rocas Verdes Basin in the Cretaceous is linked to the high-grade metamorphism of Cordillera Darwin Metamorphic Complex in southern Tierra del Fuego.

As the Andean orogeny went on, South America drifted away from Antarctica during the Cenozoic leading first to the formation of an isthmus and then to the opening of the Drake Passage 45 million years ago. The separation from Antarctica changed the tectonics of the Fuegian Andes into a transpressive regime with transform faults.

About 15 million years ago in the Miocene the Chile Ridge begun to subduct beneath the southern tip of Patagonia (55° S). The point of subduction, the triple junction has gradually moved to the north and lies at present at 47° S. The subduction of the ridge has created a northward moving "window" or gap in the asthenosphere beneath South America.

Geology of the Appalachians

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Geology_of_the_Appalachians
 
The "Pennsylvania Salient" in the Appalachians, appears to have been formed by a large, dense block of mafic volcanic rocks that became a barrier and forced the mountains to push up around it. 2012 image from NASA's Aqua satellite.
 
Generalized east-to-west cross section through the central Hudson Valley region. USGS image.
 
The geology of the Appalachians dates back to more than 480 million years ago. A look at rocks exposed in today's Appalachian Mountains reveals elongate belts of folded and thrust faulted marine sedimentary rocks, volcanic rocks and slivers of ancient ocean floor – strong evidence that these rocks were deformed during plate collision. The birth of the Appalachian ranges marks the first of several mountain building plate collisions that culminated in the construction of the supercontinent Pangaea with the Appalachians and neighboring Little Atlas (now in Morocco) near the center. These mountain ranges likely once reached elevations similar to those of the Alps and the Rocky Mountains before they were eroded.

Geological history


Paleozoic Era

Paleogeographic reconstruction showing the Appalachian Basin area during the Middle Devonian period.
 
During the earliest Paleozoic Era, the continent that would later become North America straddled the equator. The Appalachian region was a passive plate margin, not unlike today's Atlantic Coastal Plain Province. During this interval, the region was periodically submerged beneath shallow seas. Thick layers of sediment and carbonate rock were deposited on the shallow sea bottom when the region was submerged. When seas receded, terrestrial sedimentary deposits and erosion dominated.

During the Middle Ordovician Period (about 458-470 million years ago), a change in plate motions set the stage for the first Paleozoic mountain building event (Taconic orogeny) in North America. The once quiet Appalachian passive margin changed to a very active plate boundary when a neighboring oceanic plate, the Iapetus, collided with and began sinking beneath the North American craton. With the creation of this new subduction zone, the early Appalachians were born.

Along the continental margin, volcanoes grew, coincident with the initiation of subduction. Thrust faulting uplifted and warped older sedimentary rock laid down on the passive margin. As mountains rose, erosion began to wear them down. Streams carried rock debris downslope to be deposited in nearby lowlands.

This was just the first of a series of mountain building plate collisions that contributed to the formation of the Appalachians. Mountain building continued periodically throughout the next 250 million years (Caledonian, Acadian, Ouachita, Hercynian, and Alleghenian orogenies). Continent after continent was thrust and sutured onto the North American craton as the Pangean supercontinent began to take shape. Microplates, smaller bits of crust, too small to be called continents, were swept in, one by one, to be welded to the growing mass.

By about 300 million years ago (Pennsylvanian Period) Africa was approaching the North American craton. The collisional belt spread into the Ozark-Ouachita region and through the Marathon Mountains area of Texas. Continent vs. continent collision raised the Appalachian-Ouachita chain to a lofty mountain range on the scale of the present-day Himalaya. The massive bulk of Pangea was completed near the end of the Paleozoic Era (Permian Period) when Africa (Gondwana) plowed into the continental agglomeration, with the Appalachian-Ouachita mountains near the core.

Mesozoic Era and later

Pangea began to break up about 220 million years ago, in the Early Mesozoic Era (Late Triassic Period). As Pangea rifted apart a new passive tectonic margin was born and the forces that created the Appalachian, Ouachita, and Marathon Mountains were stilled. Weathering and erosion prevailed, and the mountains began to wear away.

By the end of the Mesozoic Era, the Appalachian Mountains had been eroded to an almost flat plain. It was not until the region was uplifted during the Cenozoic Era that the distinctive topography of the present formed. Uplift rejuvenated the streams, which rapidly responded by cutting downward into the ancient bedrock. Some streams flowed along weak layers that define the folds and faults created many millions of years earlier. Other streams downcut so rapidly that they cut right across the resistant folded rocks of the mountain core, carving canyons across rock layers and geologic structures. The ridges of the Appalachian Mountain core represent erosion-resistant rock that remained after the rock above and beside it was eroded away.

Geologic provinces

Map of Appalachian geological provinces

The Appalachian Mountains span across five geologic provinces (as defined by the USGS): the Appalachian Basin, the Blue Ridge Mountains, the Piedmont Province, the Adirondack Province, and the New England Province.

The Appalachian Basin

The Appalachian Basin is a foreland basin containing Paleozoic sedimentary rocks of Early Cambrian through Early Permian age. From north to south, the Appalachian Basin Province crosses New York, Pennsylvania, eastern Ohio, West Virginia, western Maryland, eastern Kentucky, western Virginia, eastern Tennessee, northwestern Georgia, and northeastern Alabama. The northern end of the Appalachian Basin extends offshore into Lakes Erie and Ontario as far as the United States–Canada border. The Appalachian Basin province covers an area of about 185,500 square miles (480,000 km2). The province is 1,075 miles (1,730 km) long from northeast to southwest and between 20 to 310 miles (30 to 500 km) wide from northwest to southeast.

The northwestern flank of the basin is a broad homocline that dips gently southeastward off the Cincinnati Arch. A complexly thrust faulted and folded terrane (Appalachian Fold and Thrust Belt or Eastern Overthrust Belt), formed at the end of the Paleozoic by the Alleghenian orogeny, characterizes the eastern flank of the basin. Metamorphic and igneous rocks of the Blue Ridge Thrust Belt that bounds the eastern part of the Appalachian Basin Province were thrust westward more than 150 miles (240 km) over lower Paleozoic sedimentary rocks.

Coal, oil, and gas production

The Appalachian Basin is one of the most important coal producing regions in the US and one of the biggest in the world. Appalachian Basin bituminous coal has been mined throughout the last three centuries. Currently, the coal primarily is used within the eastern U.S. or exported for electrical power generation, but some of it is suitable for metallurgical uses. Economically important coal beds were deposited primarily during Pennsylvanian time in a southeastward-thickening foreland basin. Coal and associated rocks form a clastic wedge that thickens from north to south, from Pennsylvania into southeast West Virginia and southwestern Virginia.

The Appalachian Basin has had a long history of oil and gas production. Discovery of oil in 1859 in the Drake Well, Venango County, Pennsylvania, marked the beginning of the oil and gas industry in the Appalachian Basin. The discovery well opened a prolific trend of oil and gas fields, producing from Upper Devonian, Mississippian, and Pennsylvanian sandstone reservoirs, that extends from southern New York, across western Pennsylvania, central West Virginia, and eastern Ohio, to eastern Kentucky.

A second major trend of oil and gas production in the Appalachian Basin began with the discovery in 1885 of oil and gas in Lower Silurian Clinton sandstone reservoirs in Knox County, Ohio. By the late 1880s and early 1900s, the trend extended both north and south across east-central Ohio and included several counties in western New York where gas was discovered in Lower Silurian Medina Group sandstones. About 1900, large oil reserves were discovered in Silurian and Devonian carbonate reservoirs in east-central Kentucky. Important gas discoveries from the Lower Devonian Oriskany Sandstone in Cambridge County, Ohio, in 1924, Schuyler County, New York, in 1930, and Kanawha County, West Virginia, in 1936 opened a major gas-producing trend across parts of New York, Pennsylvania, Maryland, Ohio, West Virginia, Kentucky, and Virginia.

Another drilling boom in the Appalachian Basin occurred in the 1960s in Morrow County, Ohio, where oil was discovered in the Upper Cambrian part of the Knox Dolomite.

Crystalline Appalachians

Geological map of the southern Crystalline Appalachians

The Blue Ridge, Piedmont, Adirondack, and New England Provinces are collectively known as the Crystalline Appalachians, because they consist of Precambrian and Cambrian igneous and metamorphic rocks.

The Blue Ridge Thrust Belt Province underlies parts of eight states from central Alabama to southern Pennsylvania. Along its western margin, the Blue Ridge is thrust over the folded and faulted margin of the Appalachian basin, so that a broad segment of Paleozoic strata extends eastward for tens of miles, buried beneath these subhorizontal crystalline thrust sheets. At the surface, the Blue Ridge consists of a mountainous to hilly region, the main component of which are the Blue Ridge Mountains that extend from Georgia to Pennsylvania. Surface rocks consist mainly of a core of moderate-to high-rank crystalline metamorphic or igneous rocks, which, because of their superior resistance to weathering and erosion, commonly rise above the adjacent areas of low-grade metamorphic and sedimentary rock. The province is bounded on the north and west by the Paleozoic strata of the Appalachian Basin Province and on the south by Cretaceous and younger sedimentary rocks of the Gulf Coastal Plain. It is bounded on the east by metamorphic and sedimentary rocks of the Piedmont Province.

The Adirondack and New England Provinces include sedimentary, metasedimentary, and plutonic igneous rocks, mainly of Cambrian and Ordovician age, similar lithologically to rocks in the Blue Ridge and Piedmont Provinces to the south. The uplifted, nearly circular Adirondack Mountains consist of a core of ancient Precambrian rocks that are surrounded by upturned Cambrian and Ordovician sedimentary rocks.

Introduction to entropy

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