Rift zone

A rift zone is a feature of some volcanoes, especially shield volcanoes, in which a set of linear cracks (or rifts) develops in a volcanic edifice, typically forming into two or three well-defined regions along the flanks of the vent.[1] Believed to be primarily caused by internal and gravitational stresses generated by magma emplacement within and across various regions of the volcano, rift zones allow the intrusion of magmatic dykes into the slopes of the volcano itself. The addition of these magmatic materials usually contributes to the further rifting of the slope, in addition to generating fissure eruptions from those dykes that reach the surface. It is the grouping of these fissures, and the dykes that feed them, that serves to delineate where and whether a rift zone is to be defined.[2] The accumulated lava of repeated eruptions from rift zones along with the endogenous growth created by magma intrusions causes these volcanoes to have an elongated shape.[3] Perhaps the best example of this is Mauna Loa, which in Hawaiian means "long mountain",[4] and which features two very well defined rift zones extending tens of kilometers outward from the central vent.

East rift zone kilauea
East Rift Zone on Kīlauea, Hawaiʻi

Formation

Rift zones are characterized by the close grouping of intrusive dykes and extrusive fissures extending outward along a relatively narrow band from the area of a central vent. The internal extensional forces and isostatic loading generated by intruding magma volumes (either associated with the magma chamber or subsequent dyke and sill formation extending outward from that chamber), in conjunction with accumulation of erupted materials, contribute to the mass and slope of the forming edifice. It is the weight of the edifice exceeding its material strength, with the additional stresses of the magma inflating the internal regions of the edifice, that can generate the initial cracking around a developing volcanic summit.[2] Additionally, tectonic activity such as normal faulting is also commonly associated with formation of rifts along volcanic flanks.[2][5] Following the path of least resistance, subsequent magmatic dykes form along and within these initial cracks, causing additional stresses to be imparted to the local materials of the edifice, which in turn generate new rifts for the magma to flow towards.[1][6] In this way, established rift zones can potentially be self-sustaining geologic features along the flanks of the given volcanic vent. The orientation of this rifting is largely dependent on the gravitational and tectonic stresses at play. Basaltic shield volcanoes typically feature two main rift zones, situated with angles of 120° between in ideal situations.[1][3] On shield volcanoes forming from level seafloor without neighboring vents, flank rifting occurs more evenly distributed around the vent.[1] However, where the flanks of a volcano may be supported on one side by the presence of a pre-existing feature, or burdened with various planes of weakness, rift zone formation promulgates according to down-slope pull of gravity.

Structure

The infill of magmas in the form of dykes helps to define the shape of a volcano. A higher frequency of intrusive events along rift zones leads to elongated topographies of the affected edifices.[6] Mathematical models show how the presence of rift zones contributes to a central horizontal bulge or ridge parallel to the orientation of the rifts.[3] This same modelling shows how this central bulge is dependent on the ration between rift zone length and depth of the magma sources, with longer fissures over shallower sources being more positively associated with very elongated topographies of the associated flanks.[3] Occasionally, fissure eruptions associated with rift zones can actually evolve into new vents along the volcanic edifice, generating lava flows lasting for months or longer.[1] These lava flows add surface materials to the slopes of the volcano, extending the slopes outward in a general flattening of the morphology of the flank.[6] The extensional character of these events can contribute to flank instability and mass wasting events where whole sections of the volcanic edifice can collapse along rift zone boundaries.[5] These mass wasting events can affect the dyke formations and orientations as the mass of the edifice shifts, which can have profound impacts on the structural development of the edifice,[5] while also potentially creating many volcanic hazards, such as tsunamis and dramatic shifts in directions of lava flows, to unsuspecting communities.

Volcanologist George P.L. Walker stated that rift zones were common in most volcanoes around the world, regardless of their type and formation.[2] Walker put forward the idea that, absent any obvious signs of rifting on the surface, the presence of other volcanic features that are also associated with dyke intrusions (such as elongated cinder cones and linearly-aligned fissure vents) should also be taken to represent the presence of a rift zone-like processes in the given region.[2] Therefore, rift zones of various lengths and widths can be tentatively identified on many stratovolcanoes and monogenetic lava fields in addition to classic Hawaiian shield volcanoes.

Examples

See also

References

  1. ^ a b c d e W., Hazlett, Richard (2010-05-17). Volcanoes : global perspectives. Wiley-Blackwell. ISBN 9781405162500. OCLC 892899076.
  2. ^ a b c d e Walker, George P. L. (1999-12-01). "Volcanic rift zones and their intrusion swarms". Journal of Volcanology and Geothermal Research. 94 (1–4): 21–34. doi:10.1016/S0377-0273(99)00096-7.
  3. ^ a b c d Annen, C.; Lénat, J. -F.; Provost, A. (2001-03-01). "The long-term growth of volcanic edifices: numerical modelling of the role of dyke intrusion and lava-flow emplacement". Journal of Volcanology and Geothermal Research. 105 (4): 263–289. doi:10.1016/S0377-0273(00)00257-2.
  4. ^ ""Mauna Loa: Earth's Largest Volcano". USGS. 2 February 2006. Retrieved 21 October 2015".
  5. ^ a b c Walter, T. R.; Troll, V. R.; Cailleau, B.; Belousov, A.; Schmincke, H.-U.; Amelung, F.; Bogaard, P. v d (2005-04-01). "Rift zone reorganization through flank instability in ocean island volcanoes: an example from Tenerife, Canary Islands" (PDF). Bulletin of Volcanology. 67 (4): 281–291. doi:10.1007/s00445-004-0352-z. ISSN 0258-8900.
  6. ^ a b c Michon, Laurent; Cayol, Valérie; Letourneur, Ludovic; Peltier, Aline; Villeneuve, Nicolas; Staudacher, Thomas (2009-07-01). "Edifice growth, deformation and rift zone development in basaltic setting: Insights from Piton de la Fournaise shield volcano (Réunion Island)". Journal of Volcanology and Geothermal Research. Recent advances on the geodynamics of Piton de la Fournaise volcano. 184 (1–2): 14–30. doi:10.1016/j.jvolgeores.2008.11.002.

External links

1975 eruption of Mauna Loa

The 1975 eruption of Mauna Loa was a short-lived Hawaiian eruption that followed 25 years of quiescence at the Hawaiian volcano Mauna Loa. The eruption began just before midnight on July 5 and involved fissures extending across the length of Moku‘āweoweo, Mauna Loa's summit caldera, and into the upper ends of the volcano's northeast and southwest rift zones. After only 6 hours, activity in Moku‘āweoweo and on the southwest rift zone ended, but lava fountaining continued along the northeast rift zone until 7:30 p.m. on July 6, when all activity ceased.

2018 lower Puna eruption

The 2018 lower Puna eruption was a volcanic event on the island of Hawaiʻi, on Kīlauea volcano's East Rift Zone that began on May 3, 2018. It is related to the larger eruption of Kīlauea that began on January 3, 1983, though some volcanologists and USGS scientists have discussed whether to classify it as a new eruption. Outbreaks of lava fountains up to 300 feet (90 m) high, lava flows, and volcanic gas in the Leilani Estates subdivision were preceded by earthquakes and ground deformation that created cracks in the roads.

On May 4, a 6.9 magnitude earthquake hit Puna. By May 27, 2018, 24 fissures had erupted lava in and near the Leilani Estates and Lanipuna Gardens subdivisions. The eruption forced the evacuation of approximately two thousand residents. The Puna Geothermal Venture, which provided one-quarter of the island's electricity, was forced to shut down and was later damaged by lava. The fissures had sent lava rivers that buried part of Hawaii Route 137 on May 19, and began flowing into the ocean.On May 29, lava from a new northeastern flow overran Hawaii Route 132, cutting the access between Kapoho and Pāhoa. The massive lava flow reached the Pacific Ocean at Kapoho Bay on June 4. Lava entered the Kapoho Crater and evaporated Green Lake, the largest natural freshwater lake in Hawai'i. On the night of June 4–5, the northeastern flow of lava speedily moved forward and destroyed the subdivision of Vacationland Hawaii. By June 5, Kapoho Bay had been filled in with lava now forming a point where the bay had been. The volcanic activity was the most destructive in the United States since the 1980 eruption of Mount St. Helens.By August 7, 13.7 square miles (35 km2) of land had been covered by lava flows. About 875 acres (3.54 km2) of new land has been created in the ocean. The official number of houses destroyed by the eruption reached 700 on July 9. It was estimated that recovery efforts would cost more than $800 million (2018 USD). By early August the eruption had almost completely subsided, and on December 5, it was declared to have ended after three months of inactivity.

Amurian Plate

The Amurian Plate (or Amur Plate; also occasionally referred to as the China Plate) is a minor tectonic plate in the northern and eastern hemispheres. It covers Manchuria, the Korean Peninsula, the Yellow Sea, and Primorsky Krai. Once thought to be a part of the Eurasian Plate, the Amur Plate is now generally considered to be a separate plate moving southeast with respect to the Eurasian Plate.

The Amurian Plate is named after the Amur River, that forms the border between the Russian Far East and Northeastern China.

It is bounded on the north, west, and southwest by the Eurasian Plate, on the east by the Okhotsk Plate, to the southeast by the Philippine Sea Plate along the Suruga Trough and the Nankai Trough, and the Okinawa Plate, and the Yangtze Plate.The Baikal Rift Zone is considered a boundary between the Amurian Plate and the Eurasian Plate. GPS measurements indicate that the plate is slowly rotating counterclockwise.

The Amurian Plate may have been involved in the 1976 Tangshan earthquake in China.

Ancient lake

An ancient lake is a lake that has consistently carried water for more than one million years. Many have existed for more than 2.6 million years, the full Quaternary period. Ancient lakes continue to persist due to plate tectonics in an active rift zone. This active rift zone creates lakes that are extremely deep and difficult to naturally fill with sediment. Due to the prolonged life of ancient lakes, they serve as models for isolated evolutionary traits and speciation.

Lake Baikal is often considered the oldest, as clear evidence shows that it is 25–30 million years old. Lake Zaysan may be even older, of Cretaceous origin and at least 65 million years old (most likely around 70 million years), but its exact age is controversial and labelled with some uncertainty. Another contender for oldest is Lake Maracaibo, estimated to be 20–36 million years old. In ancient times it was indisputably a true lake, but today it is saline and directly connected to the sea, leading many to consider it a large lagoon or bay.

Aulacogen

An aulacogen is a failed arm of a triple junction. Aulacogens are a part of plate tectonics where oceanic and continental crust is continuously being created, destroyed, and rearranged on the Earth’s surface. Specifically, aulacogens are a rift zone, where new crust is formed, that is no longer active.

Baikal Rift Zone

The Baikal Rift Zone is a series of continental rifts centered beneath Lake Baikal in southeastern Russia. Current strain in the rifts tends to be extending with some shear movement. A series of basins form along the zone for more than 2,000 kilometres (1,200 mi), creating a rift valley. The rifts form between the Eurasian Plate to the west and the Amur Plate to the east.

Cuddy Valley, California

Cuddy Valley is a valley in the San Andreas Rift Zone south of the San Emigdio Mountains west of Tejon Pass, and unincorporated community in Kern County, California, and part of the Mountain Communities. It lies at an elevation of 5,282 feet 1610 m).

Danakil Alps

The Danakil Alps are a highland region in Ethiopia and Eritrea with peaks over 1000 metres in height and a width varying between 40 and 70 kilometres. The alps lie to the east of the Danakil Depression and separate it from the southern Red Sea. A rift escarpment facing the Red Sea forms the eastern boundary of the range.

Geologically these highlands are described as a horst and are sometimes referred to as the Danakil Horst or Danakil Block. They were formed by geological faulting which has occurred since the Miocene epoch. There is Precambrian basement rock underlying the region and in coastal Eritrea Precambrian and Mesozoic rocks are exposed. The basement rock of the alps has become overlaid with flood basalt since the Oligocene epoch. About 20 million years ago the Afar rift zone opened up. This resulted in the alps breaking away from the Ethiopian plateau to which they had previously been attached and drifting to the east/northeast.The Danakil Alps contains many volcanic edifices, such as those forming the Nabro Volcanic Range. The largest of the Nabro Volcanic Range edifices are the Mallahle, Nabbro, and Dubbi. The volcanic range extends northwestward to the Red Sea, ending with the Kod Ali volcano offshore.The Danakil Alps have been cut off from the sea since the late Pleistocene.

Devana Chasma

Devana Chasma is a weak extensional rift zone on Venus, with a length of 4000 km, a width of 150–250 km, and a depth reaching 5 km. Most of the faults are facing north-south. The rift is located in Beta Regio, a 3000 km rise created by volcanic activity. Mantle plumes rising from the bottom are the reason behind the formation of the rift zone. The slow extension rates in the rift may be driven by the same reason.

East African Rift

The East African Rift (EAR) or East African Rift System (EARS) is an active continental rift zone in East Africa. The EAR began developing around the onset of the Miocene, 22–25 million years ago. In the past it was considered to be part of a larger Great Rift Valley that extended north to Asia Minor.

The rift, a narrow zone, is a developing divergent tectonic plate boundary where the African Plate is in the process of splitting into two tectonic plates, called the Somali Plate and the Nubian Plate, at a rate of 6–7 mm (0.24–0.28 in) annually. As extension continues, lithospheric rupture will occur within 10 million years; the Somali Plate will break off and a new ocean basin will form.

Gulf of California Rift Zone

The Gulf of California Rift Zone (GCRZ) is the northernmost extension of the East Pacific Rise which extends some 1,300 km (800 mi) from the mouth of the Gulf of California to the southern terminus of the San Andreas Fault at the Salton Sink.

The GCRZ is an incipient rift zone akin to the Red Sea Rift. In the GCRZ continental crust originally associated with the North American Plate has been pulled apart by tectonic forces and is being replaced by newly formed oceanic crust and seafloor spreading. The rifting has resulted in the transfer of the Baja California Peninsula to the Pacific Plate.

Kaʻū Desert

The Kaʻū Desert is a leeward desert in the district of Kaʻū, the southernmost district on the Big Island of Hawaii, and is made up mostly of dried lava remnants, volcanic ash, sand and gravel. The desert covers an area of the Kīlauea Volcano along the Southwest rift zone. The area lacks any vegetation, mainly due to acid rainfall.

Kīlauea

Kīlauea (, US: ; Hawaiian: [kiːlɐwˈwɛjə]) is an active shield volcano in the Hawaiian Islands that last erupted between 1983 and 2018. Historically, Kīlauea is the most active of the five volcanoes that together form the island of Hawaiʻi. Located along the southerneastern shore of the island, the volcano is between 210,000 and 280,000 years old and emerged above sea level about 100,000 years ago.

It is the second youngest product of the Hawaiian hotspot and the current eruptive center of the Hawaiian–Emperor seamount chain. Because it lacks topographic prominence and its activities historically coincided with those of Mauna Loa, Kīlauea was once thought to be a satellite of its much larger neighbor. Structurally, Kīlauea has a large, fairly recently formed caldera at its summit and two active rift zones, one extending 125 km (78 mi) east and the other 35 km (22 mi) west, as an active fault of unknown depth moving vertically an average of 2 to 20 mm (0.1 to 0.8 in) per year.

Kīlauea erupted nearly continuously from 1983 to 2018, causing considerable property damage, including the destruction of the towns of Kalapana in 1990, and Vacationland Hawaii and Kapoho in 2018. During the 2018 lower Puna eruption, which began on May 3, two dozen lava vents erupted downrift from the summit in Puna. The eruption was accompanied by a strong earthquake on May 4 of Mw 6.9, and nearly 2,000 residents were evacuated from the rural Leilani Estates subdivision and nearby areas.

On May 17, 2018 at 4:17 AM, the volcano explosively erupted at the summit in Halemaʻumaʻu, throwing ash 30,000 feet into the air. Continued explosive activity at the summit caused a months-long closure of the Kīlauea section of Hawaii Volcanoes National Park. Vigorous eruptive lava fountains in lower Puna sent destructive rivers of molten rock into the ocean in three places. The lava destroyed Hawaii's largest natural freshwater lake, covered substantial portions of Leilani Estates and Lanipuna Gardens, and completely inundated the communities of Kapoho, Vacationland Hawaii and all but three houses in the Kapoho Beach Lots. Lava also filled Kapoho Bay and extended new land nearly a mile into the sea. The County of Hawaii reported that 716 dwellings were destroyed by lava. By early August the eruption subsided substantially, and the last active lava was reported at the surface on September 4, 2018. Portions of Hawaii Volcanoes National Park reopened to the public on September 22. On December 5, 2018, after 90 days of inactivity from the volcano, the eruption that started in 1983 was declared to be over.

List of seismic faults in Mexico

List of seismic fault (and systems, zones) in Mexico

Mauna Ulu

Mauna Ulu is a volcanic cone in the eastern rift zone of the Kīlauea volcano on the island of Hawaii. It falls within the bounds of Hawaiʻi Volcanoes National Park. Mauna Ulu was in a state of eruption from May 1969 to July 1974.

Māhukona

Māhukona is a submerged shield volcano on the northwestern flank of the Island of Hawaiʻi. A drowned coral reef at about 3,770 feet (-1,150 m) below sea level and a major break in slope at about 4,400 feet (-1,340 m) below sea level represent old shorelines. The summit of the shield volcano was once 800 feet (250 m) above sea level. It has now subsided below sea level. A roughly circular caldera marks the summit of Māhukona. A prominent rift zone extends to the west. A second rift zone probably extended to the east but has been buried by younger volcanoes. The main shield-building stage of volcanism ended about 470,000 years ago. The summit of the shield volcano subsided below sea level between 435,000 and 365,000 years ago.

This makes Māhukona the oldest volcano to build Hawaiʻi island, compared to Kohala to the east and Mauna Kea to the east. The Monterey Bay Aquarium Research Institute investigated the area with a remotely controlled submarine in 2001.It was named for the area known as Māhukona, on the shore to the northeast.

Ozza Mons

Ozza Mons is an inactive volcano on planet Venus near the equator.Four temporally variable surface hotspots were discovered at the Ganiki Chasma rift zone near volcanoes Ozza Mons and Maat Mons in 2015, suggestive of present volcanic activity. However, interpreting these types of observations from above the cloud layer correctly is a challenge.

Puʻu ʻŌʻō

Puʻu ʻŌʻō (often written Puu Oo, pronounced [ˈpuʔu ˈʔoːʔoː], poo-oo oh-oh) is a volcanic cone in the eastern rift zone of the Kīlauea volcano of the Hawaiian Islands. Until the end of April 2018, Puʻu ʻŌʻō had been erupting nearly continuously since January 3, 1983, making it the longest-lived rift-zone eruption of the last two centuries.By January 2005, 2.7 cubic kilometers (0.65 cu mi) of magma covered an area of more than 117 square kilometers (45 sq mi) and added 230 acres (0.93 km2) of land to the southeast coast of Hawaiʻi. The eruption claimed at least 189 buildings and 14 kilometers (8.7 mi) of highways, as well as a church, a store, the Wahaʻula Visitor Center, and many ancient Hawaiian sites, including the Wahaʻula heiau. The coastal highway has been closed since 1987, as parts of the road have been buried under lava up to 35 meters (115 ft) thick.

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