Iceland is one of the most active volcanic regions in the world, with eruptions occurring on average roughly every three years (in the 20th century there were 39 volcanic eruptions on and around Iceland). About a third of the basaltic lavas erupted in recorded history have been produced by Icelandic eruptions. Notable eruptions have included that of Eldgjá, a fissure of Katla, in 934 (the world's largest basaltic eruption ever witnessed), Laki in 1783 (the world's second largest), and several eruptions beneath ice caps, which have generated devastating glacial bursts, most recently in 2010 after the eruption of Eyjafjallajökull.
Iceland's location astride the Mid-Atlantic Ridge, where the Eurasian and North American Plates are moving apart, is partly responsible for this intense volcanic activity, but an additional cause is necessary to explain why Iceland is a substantial island while the rest of the ridge mostly consists of seamounts, with peaks below sea level.
As well as being a region of higher temperature than the surrounding mantle, it is believed to have a higher concentration of water. The presence of water in magma reduces the melting temperature, which may also play a role in enhancing Icelandic volcanism.
There is an ongoing discussion about whether the hotspot is caused by a deep mantle plume or originates at a much shallower depth. Recently, seismic tomography studies have found seismic wave speed anomalies under Iceland, consistent with a hot conduit 100 km across that extends to the lower mantle.
Some geologists have questioned whether the Iceland hotspot has the same origin as other hotspots, such as the Hawaii hotspot. While the Hawaiian island chain and the Emperor Seamounts show a clear time-progressive volcanic track caused by the movement of the Pacific Plate over the Hawaiian hotspot, no such track can be seen at Iceland.
It is proposed that the line from Grímsvötn volcano to Surtsey shows the movement of the Eurasian Plate, and the line from Grímsvötn volcano to Reykjanes volcanic belt shows the movement of the North American Plate.
The Iceland plume is a postulated upwelling of anomalously hot rock in the Earth's mantle beneath Iceland. Its origin is thought to lie deep in the mantle, perhaps at the boundary between the core and the mantle at approximately 2,880 km depth. Opinions differ as to whether seismic studies have imaged such a structure. In this framework, the volcanism of Iceland is attributed to this plume, according to the theory of W. Jason Morgan.
It is believed that a mantle plume underlies Iceland, of which the hotspot is thought to be the surface expression, and that the presence of the plume enhances the volcanism already caused by plate separation. Additionally, flood basalts on the continental margins of Greenland and Norway, the oblique orientation of the Reykjanes Ridge segments to their spreading direction, and the enhanced igneous crustal thickness found along the southern Aegir and Kolbeinsey Ridges may be results of interaction between the plume and the Mid-Atlantic Ridge. The plume stem is believed to be quite narrow, perhaps 100 km across and extending down to at least 400–650 km beneath the Earth's surface, and possibly down to the core-mantle boundary, while the plume head may be > 1,000 km in diameter.
It is suggested that the lack of a time-progressive track of seamounts is due to the location of the plume beneath the thick Greenland craton for ~ 15 Myr after continental breakup, and the later entrenchment of the plume material into the northern Mid-Atlantic Ridge following its formation.
According to the plume model, the source of Icelandic volcanism lies deep beneath the center of the island. The earliest volcanic rocks attributed to the plume are found on both sides of the Atlantic. Their ages have been determined to lie between 58 and 64 million years. This coincides with the opening of the north Atlantic in the late Paleocene and early Eocene, which has led to suggestions that the arrival of the plume was linked to, and has perhaps contributed to, the breakup of the North Atlantic continent. In the framework of the plume hypothesis, the volcanism was caused by the flow of hot plume material initially beneath thick continental lithosphere and then beneath the lithosphere of the growing ocean basin as rifting proceeded. The exact position of the plume at that time is a matter of disagreement between scientists, as is whether the plume is thought to have ascended from the deep mantle only at that time or whether it is much older and also responsible for the old volcanism in northern Greenland, on Ellesmere Island, and at Alpha Ridge in the Arctic.
As the northern Atlantic opened to the east of Greenland during the Eocene, North America and Eurasia drifted apart; the Mid-Atlantic Ridge formed as an oceanic spreading center and a part of the submarine volcanic system of mid-oceanic ridges. The initial plume head may have been several thousand kilometers in diameter, and it erupted volcanic rocks on both sides of the present ocean basin to produce the North Atlantic Igneous Province. Upon further opening of the ocean and plate drift, the plume and the mid-Atlantic Ridge are postulated to have approached one another, and finally met. The excess magmatism that accompanied the transition from flood volcanism on Greenland, Ireland and Norway to present-day Icelandic activity was the result of ascent of the hot mantle source beneath progressively thinning lithosphere, according to the plume model, or a postulated unusually productive part of the mid-ocean ridge system. Some geologists have suggested that the Iceland plume could have been responsible for the Paleogene uplift of the Scandinavian Mountains by producing changes in the density of the lithosphere and asthenosphere during the opening of the North Atlantic. To the south the Paleogene uplift of the English chalklands that resulted in the formation of the Sub-Paleogene surface has also been attributed to the Iceland plume.
An extinct ridge exists in western Iceland, leading to the theory that the plume has shifted east with time. The oldest crust of Iceland is more than 20 million years old and was formed at an old oceanic spreading center in the Westfjords (Vestfirðir) region. The westward movement of the plates and the ridge above the plume and the strong thermal anomaly of the latter caused this old spreading center to cease 15 million years ago and lead to the formation of a new one in the area of today's peninsulas Skagi and Snæfellsnes; in the latter there is still some activity in the form of the Snæfellsjökull volcano. The spreading center, and hence the main activity, have shifted eastward again 7–9 million years ago and formed the current volcanic zones in the southwest (Reykjanes, Hofsjökull) and northeast (Tjörnes). Presently, a slow decrease of the activity in the northeast takes place, while the volcanic zone in the southeast (Katla, Vatnajökull), which was initiated 3 million years ago, develops. The reorganisation of the plate boundaries in Iceland has also been attributed to microplate tectonics.
The weak visibility of the postulated plume in tomographic images of the lower mantle and the geochemical evidence for eclogite in the mantle source have led to the theory that Iceland is not underlain by a mantle plume at all, but that the volcanism there results from processes related to plate tectonics and is restricted to the upper mantle.
According to one of those models, a large chunk of the subducted plate of a former ocean has survived in the uppermost mantle for several hundred million years, and its oceanic crust now causes excessive melt generation and the observed volcanism. This model, however, is not backed by dynamical calculations, nor is it exclusively required by the data, and it also leaves unanswered questions concerning the dynamical and chemical stability of such a body over that long period or the thermal effect of such massive melting.
Another model proposes that the upwelling in the Iceland region is driven by lateral temperature gradients between the suboceanic mantle and the neighbouring Greenland craton and therefore also restricted to the upper 200–300 km of the mantle. However, this convection mechanism is probably not strong enough under the conditions prevailing in the north Atlantic, with respect to the spreading rate, and it does not offer a simple explanation for the observed geoid anomaly.
Information about the structure of Earth's deep interior can be acquired only indirectly by geophysical and geochemical methods. For the investigation of postulated plumes, gravimetric, geoid and in particular seismological methods along with geochemical analyses of erupted lavas have proven especially useful. Numerical models of the geodynamical processes attempt to merge these observations into a consistent general picture.
An important method for imaging large-scale structures in Earth's interior is seismic tomography, by which the area under consideration is "illuminated" from all sides with seismic waves from earthquakes from as many different directions as possible; these waves are recorded with a network of seismometers. The size of the network is crucial for the extent of the region which can be imaged reliably. For the investigation of the Iceland Plume, both global and regional tomography have been used; in the former, the whole mantle is imaged at relatively low resolution using data from stations all over the world, whereas in the latter, a denser network only on Iceland images the mantle down to 400–450 km depth with higher resolution.
Regional studies from the 1990s and 2000s show that there is a low seismic-wave-speed anomaly beneath Iceland, but opinion is divided as to whether it continues deeper than the mantle transition zone at roughly 600 km depth. The velocities of seismic waves are reduced by up to 3% (P waves) and more than 4% (S waves), respectively. These values are consistent with a small percentage of partial melt, a high magnesium content of the mantle, or elevated temperature. It is not possible to unambiguously separate out which effect causes the observed velocity reduction.
Numerous studies have addressed the geochemical signature of the lavas present on Iceland and in the north Atlantic. The resulting picture is consistent in several important respects. For instance, it is not contested that the source of the volcanism in the mantle is chemically and petrologically heterogeneous: it contains not only peridotite, the principal mantle rock type, but also eclogite, a rock type that originates from the basalt in subducted slabs and is more easily fusible than peridotite. The origin of the latter is assumed to be metamorphosed, very old oceanic crust which sank into the mantle several hundreds of millions of years ago during the subduction of an ocean, then upwelled from deep within the mantle.
Studies using the major and trace-element compositions of Icelandic volcanics showed that the source of present-day volcanism was about 100 °C greater than that of the source of mid-ocean ridge basalts.
The variations in the concentrations of trace elements such as helium, lead, strontium, neodymium, and others show clearly that Iceland is compositionally distinct from the rest of the north Atlantic. For instance, the ratio of He-3 and He-4 has a pronounced maximum on Iceland, which correlates well with geophysical anomalies, and the decrease of this and other geochemical signatures with increasing distance from Iceland indicate that the extent of the compositional anomaly reaches about 1,500 km along the Reykjanes Ridge and at least 300 km along the Kolbeinsey Ridge. Depending on which elements are considered and how large the area covered is, one can identify up to six different mantle components, which are not all present in any single location.
Furthermore, some studies show that the amount of water dissolved in mantle minerals is two to six times higher in the Iceland region than in undisturbed parts of the mid-oceanic ridges, where it is regarded to lie at about 150 parts per million. The presence of such a large amount of water in the source of the lavas would tend to lower its melting point and make it more productive for a given temperature.
The north Atlantic is characterized by strong, large-scale anomalies of the gravity field and the geoid. The geoid rises up to 70 m above the geodetic reference ellipsoid in an approximately circular area with a diameter of several hundred kilometers. In the context of the plume hypothesis, this has been explained by the dynamic effect of the upwelling plume which bulges up the surface of the Earth. Furthermore, the plume and the thickened crust cause a positive gravity anomaly of about 60 mGal (=0.0006 m/s²) (free-air).
Since the mid-1990s several attempts have been made to explain the observations with numerical geodynamical models of mantle convection. The purpose of these calculations was, among other things, to resolve the paradox that a broad plume with a relatively low temperature anomaly is in better agreement with the observed crustal thickness, topography, and gravity than a thin, hot plume, which has been invoked to explain the seismological and geochemical observations. The most recent models prefer a plume that is 180–200 °C hotter than the surrounding mantle and has a stem with a radius of ca. 100 km. Such temperatures have not yet been confirmed by petrology, however.
The Aegir Ridge is an extinct segment of the Mid-Atlantic Ridge in the far-northern Atlantic Ocean. It marks the initial break-up boundary between Greenland and Norway, along which seafloor spreading was initiated at the beginning of the Eocene epoch to form the northern Atlantic Ocean. Towards the end of the Eocene, the newly forming Kolbeinsey Ridge propagated northwards from Iceland, splitting the Jan Mayen Microcontinent away from the Greenland Plate. As the Kolbeinsey Ridge formed, so activity on the Aegir Ridge reduced, ceasing completely at the end of the Oligocene epoch when the Kolbeinsey Ridge reached the Jan Mayen Fracture Zone.The relatively thin crust and short lifespan of the Aegir Ridge is anomalous given its proximity to the Iceland hotspot. Mantle hotspots deliver warm, actively-upwelling material to mid-ocean ridges, increasing mantle melting and crustal production. Likely, the stresses associated with plate tectonics and the mechanical structure of the lithosphere created a situation in which spreading at the Kolbeinsey Ridge was energetically favorable to spreading at the Aegir Ridge. As the Kolbeinsey Ridge began rifting, hotspot material would then draw out of the Aegir Ridge and flow preferentially towards the Kolbeinsey Ridge, leading to the ultimate extinction of the spreading center.Don L. Anderson
Don Lynn Anderson (March 5, 1933 – December 2, 2014) was an American geophysicist who made significant contributions to the understanding of the origin, evolution, structure, and composition of Earth and other planets. An expert in numerous scientific disciplines, Anderson's work combined seismology, solid state physics, geochemistry and petrology to explain how the Earth works. Anderson was best known for his contributions to the understanding of the Earth's deep interior, and more recently, for the hypothesis that hotspots are the product of plate tectonics rather than narrow plumes emanating from the deep Earth. Anderson was Professor (Emeritus) of Geophysics in the Division of Geological and Planetary Sciences at the California Institute of Technology (Caltech). He received numerous awards from geophysical, geological and astronomical societies. In 1998 he was awarded the prestigious Crafoord Prize by the Royal Swedish Academy of Sciences along with Adam Dziewonski. Later that year, Anderson received the National Medal of Science. He held honorary doctorates from Rensselaer Polytechnic Institute (where he did his undergraduate work in geology and geophysics) and the University of Paris (Sorbonne), and served on numerous university advisory committees, including those at Harvard, Princeton, Yale, University of Chicago, Stanford, University of Paris, Purdue University, and Rice University. Anderson's wide-ranging research resulted in hundreds of published papers in the fields of planetary science, seismology, mineral physics, petrology, geochemistry, tectonics and the philosophy of science. He continued to work and publish until his death. His widely known textbooks, Theory of the Earth, and New Theory of the Earth are regarded by colleagues as compelling syntheses of the origins of the Earth and its inner workings by one of the great geophysical authorities of our time.East Australia hotspot
The East Australia hotspot is a volcanic hotspot that forces magma up at weak spots in the Indo-Australian Plate to form volcanoes in Eastern Australia. It does not produce a single chain of volcanoes like the Hawaiian Islands. Unlike most hotspots, the East Australia hotspot has explosive eruptions, as well as the runny lava flows of the Hawaii hotspot, the Iceland hotspot and the Réunion hotspot. The hotspot is explosive because basaltic magma interacts with groundwater in aquifers below the surface producing violent phreatomagmatic eruptions.
Tweed Volcano in New South Wales is a large shield volcano that was formed by the hotspot about 23 million years ago and has one of the biggest erosion calderas in the world.
A number of the volcanoes in the province have erupted since Aboriginal settlement (46,000 BP). The most recent eruptions were about 5,600 years ago, and memories of them survive in Aboriginal folklore. These eruptions formed the volcanoes Mount Schank and Mount Gambier in the Newer Volcanics Province. There have been no eruptions on the Australian mainland since European settlement.Eldgjá
Eldgjá (Icelandic pronunciation: [ˈɛltcau] (listen), "fire canyon") is a volcano and a canyon in Iceland. Eldgjá and the Katla volcano are part of the same volcanic system in the south of the country.
Situated between Landmannalaugar and Kirkjubæjarklaustur, Eldgjá is the largest volcanic canyon in the world, approx. 40 km long, 270 m deep and 600 m wide at its greatest.Ellesmere Island Volcanics
The Ellesmere Island Volcanics are a Late Cretaceous volcanic group of volcanoes and lava flows in the Qikiqtaaluk Region of northern Ellesmere Island, Nunavut, Canada.
Ellesmere Island Volcanics are part of the Arctic Cordillera. This volcanic province is among the northernmost volcanism on Earth.Geography of Iceland
Iceland (Icelandic: Ísland [ˈistlant])is an island country at the confluence of the North Atlantic and Arctic Oceans, east of Greenland and immediately south of the Arctic Circle, atop the constructive boundary of the northern Mid-Atlantic Ridge about 860 km (530 mi) from Scotland and 4,200 km (2,600 mi) from New York City. One of the world's most sparsely populated countries, Iceland's boundaries are almost the same as the main island – the world's 18th largest in area and possessing almost all of the country's area and population. It is the westernmost European country with more land covered by glaciers than in all of continental Europe. The total size is 103,125 km2 (39,817 sq mi). It has an Exclusive Economic Zone of 751,345 km2 (290,096 sq mi).Geological deformation of Iceland
The geological deformation of Iceland is the way that the rocks of the island of Iceland are changing due to tectonic forces. The geological deformation explains the location of earthquakes, volcanoes, fissures, and the shape of the island. Iceland is the largest landmass (102,775 km²) situated on an oceanic ridge. It is an elevated plateau of the sea floor, situated at the crossing of the Mid-Atlantic Ridge and the Greenland-Iceland-Faeroe Ridge. It lies along the oceanic divergent plate boundary of North American Plate and Eurasian Plate. The western part of Iceland sits on the North American Plate and the eastern part sits on the Eurasian Plate. The Reykjanes Ridge of the Mid-Atlantic ridge system in this region crosses the island from southwest and connects to the Kolbeinsey Ridge in the northeast.Iceland is geologically young: all rocks there were formed within the last 25 million years. It started construction in the Early Miocene sub-epoch, but the oldest rocks found at the surface of Iceland are from the Middle Miocene sub-epoch. Nearly half of Iceland was formed from a slow spreading period from 9 to 20 million years ago (Ma).The geological structures and geomorphology of Iceland are strongly influenced by the spreading plate boundary and the Iceland hotspot. The buoyancy of the deep-seated mantle plume underneath has uplifted the Iceland Basalt Plateau to as high as 3000 meters. The hot spot also produces high volcanic activity on the plate boundary.There are two major geologic and topographic structural trends in Iceland. One strikes northeast in Southern Iceland and strikes nearly north in northern Iceland. The other one strikes approximately west-northwest. Altogether they produce a zigzag pattern. The pattern is shown by faults, volcanic fissures, valleys, dikes, volcanoes, grabens and fault scarps.Geology of Iceland
The geology of Iceland is unique and of particular interest to geologists. Iceland lies on the divergent boundary between the Eurasian plate and the North American plate. It also lies above a hotspot, the Iceland plume. The plume is believed to have caused the formation of Iceland itself, the island first appearing over the ocean surface about 16 to 18 million years ago. The result is an island characterized by repeated volcanism and geothermal phenomena such as geysers.
The eruption of Laki in 1783 caused much devastation and loss of life, leading to a famine that killed about 25% of the island's population and resulted in a drop in global temperatures, as sulfur dioxide was spewed into the Northern Hemisphere. This caused crop failures in Europe and may have caused droughts in India. The eruption has been estimated to have killed over six million people globally.Between 1963 and 1967, the new island of Surtsey was created off the southwest coast by a volcanic eruption.Grímsvötn
Grímsvötn (Icelandic pronunciation: [ˈkrimsvœʰtn̥]; vötn = "waters", singular: vatn) is a volcano in southeast Iceland. It is in the highlands of Iceland at the northwestern side of the Vatnajökull ice-cap. The caldera is at 64°25′N 17°20′W, at an elevation of 1,725 m (5,659 ft). Beneath the caldera is the magma chamber of the Grímsvötn volcano.
Grímsvötn is a basaltic volcano which has the highest eruption frequency of all the volcanoes in Iceland and has a southwest-northeast-trending fissure system. The massive climate-impacting Laki fissure eruption of 1783–1784 was a part of the same fissure system. Grímsvötn was erupting at the same time as Laki during 1783, but continued to erupt until 1785. Because most of the volcano lies underneath Vatnajökull, most of its eruptions have been subglacial and the interaction of magma and meltwater from the ice causes phreatomagmatic explosive activity.On 21 May 2011 at 19:25 UTC, an eruption began, with 12 km (7 mi) high plumes accompanied by multiple earthquakes, resulting in cancellation of 900 flights in Iceland, and in the United Kingdom, Greenland, Germany, Ireland and Norway on 22–25 May. Until 25 May, the eruption scale had been larger than that of the 2010 eruption of Eyjafjallajökull. The eruption stopped at 02:40 UTC on 25 May 2011, although there was some explosive activity from the tephra vents affecting only the area around the crater.Hotspot (geology)
In geology, the places known as hotspots or hot spots are volcanic regions thought to be fed by underlying mantle that is anomalously hot compared with the surrounding mantle. Their position on the Earth's surface is independent of tectonic plate boundaries. There are two hypotheses that attempt to explain their origins. One suggests that hotspots are due to mantle plumes that rise as thermal diapirs from the core–mantle boundary. The other hypothesis is that lithospheric extension permits the passive rising of melt from shallow depths. This hypothesis considers the term "hotspot" to be a misnomer, asserting that the mantle source beneath them is, in fact, not anomalously hot at all. Well-known examples include the Hawaii, Iceland and Yellowstone hotspots.Lava dome
In volcanology, a lava dome or volcanic dome is a roughly circular mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano. Dome-building eruptions are common, particularly in convergent plate boundary settings. Around 6% of eruptions on earth are lava dome forming. The geochemistry of lava domes can vary from basalt (e.g. Semeru, 1946) to rhyolite (e.g. Chaiten, 2010) although the majority are of intermediate composition (such as Santiaguito, dacite-andesite, present day) The characteristic dome shape is attributed to high viscosity that prevents the lava from flowing very far. This high viscosity can be obtained in two ways: by high levels of silica in the magma, or by degassing of fluid magma. Since viscous basaltic and andesitic domes weather fast and easily break apart by further input of fluid lava, most of the preserved domes have high silica content and consist of rhyolite or dacite.
Existence of lava domes has been suggested for some domed structures on the Moon, Venus, and Mars, e.g. the Martian surface in the western part of Arcadia Planitia and within Terra Sirenum.List of volcanoes in Iceland
This list of volcanoes in Iceland includes 31 active and extinct volcanic mountains, of which 18 have erupted since human settlement of Iceland began circa 900 CE.North Atlantic Igneous Province
The North Atlantic Igneous Province (NAIP) is a large igneous province in the North Atlantic, centered on Iceland. In the Paleogene, the province formed the Thulean Plateau, a large basaltic lava plain, which extended over at least 1.3 million km2 (500 thousand sq mi) in area and 6.6 million km3 (1.6 million cu mi) in volume. The plateau was broken up during the opening of the North Atlantic Ocean leaving remnants existing in Northern Ireland, bits of northwestern Scotland, the Faroe Islands, bits of northwestern Iceland, eastern Greenland and western Norway and many of the islands located in the north eastern portion of the North Atlantic Ocean. The igneous province is the origin of the Giant's Causeway and Fingal's Cave. The province is also known as Brito-Arctic province (also known as the North Atlantic Tertiary Volcanic Province) and the portions of the province in the British Isles is also called the British Tertiary Volcanic Province or British Tertiary Igneous Province.Outline of Iceland
The following outline is provided as an overview of and topical guide to Iceland:
Iceland – sovereign island nation located in the North Atlantic Ocean between continental Europe and Greenland. It is considered part of Northern Europe. It is the least populous of the Nordic countries, having a population of about 329,000 (January 1, 2015). Iceland is volcanically and geologically active on a large scale; this defines the landscape in various ways. The interior mainly consists of a plateau characterized by sand fields, mountains and glaciers, while many big glacial rivers flow to the sea through the lowlands. Warmed by the Gulf Stream, Iceland has a temperate climate relative to its latitude and provides a habitable environment and nature.Rum layered intrusion
The Rum layered intrusion is located in Scotland, on the Isle of Rum (Inner Hebrides). It is a mass of intrusive rock, of mafic-ultramafic composition, the remains of the eroded, solidified magma chamber of an extinct volcano that was active during the Palaeogene Period. It is associated with the nearby Skye intrusion and Skye, Mull and Egg lavas. It was emplaced 60 million years ago above the Iceland hotspot.Volcanology of Northern Canada
Volcanology of Northern Canada includes hundreds of volcanic areas and extensive lava formations across Northern Canada. The region's different volcano and lava types originate from different tectonic settings and types of volcanic eruptions, ranging from passive lava eruptions to violent explosive eruptions. Northern Canada has a record of very large volumes of magmatic rock called large igneous provinces. They are represented by deep-level plumbing systems consisting of giant dike swarms, sill provinces and layered intrusions.Weizhou Island
Weizhou Island (simplified Chinese: 涠洲岛; traditional Chinese: 潿洲島; pinyin: Wéizhōu Dǎo) is a Chinese island in the Gulf of Tonkin. The largest island of Guangxi Zhuang Autonomous Region, Weizhou is west of Leizhou Peninsula, south of Beihai, and east of Vietnam. Administratively, it is part of Weizhou Town, Haicheng District of Beihai City.Wen Lianxing
Wen Lianxing (Chinese: 温联星; born April 1968) is a Chinese seismologist and geophysicist. He is a professor at Stony Brook University and the University of Science and Technology of China. He was awarded the James B. Macelwane Medal in 2003 and elected a fellow of the American Geophysical Union.Yellowstone Caldera
The Yellowstone Caldera is a volcanic caldera and supervolcano in Yellowstone National Park in the Western United States, sometimes referred to as the Yellowstone Supervolcano. The caldera and most of the park are located in the northwest corner of Wyoming. The major features of the caldera measure about 34 by 45 miles (55 by 72 km).The caldera formed during the last of three supereruptions over the past 2.1 million years: the Huckleberry Ridge eruption 2.1 million years ago (which created the Island Park Caldera and the Huckleberry Ridge Tuff); the Mesa Falls eruption 1.3 million years ago (which created the Henry's Fork Caldera and the Mesa Falls Tuff); and the Lava Creek eruption approximately 630,000 years ago (which created the Yellowstone Caldera and the Lava Creek Tuff).