|
Bibliography
Compiled From: 1 Smithsonian Institution - Global Volcanism Program Web site, 1998, and 2 Wright and Pierson, 1992, Living With Volcanoes, The U. S. Geological Survey's Volcano Hazards Program: USGS Circular 1073
Yellowstone Caldera
Location: Wyoming, Montana, Idaho
Latitude: 44.43 N
Longitude: 110.67 W
Height: 2,805 Meters
Type: Calderas
Number of eruptions in past 200 years: 0
Latest Eruptions: 70,000 years ago
Present thermal activity: Numerous hydrothermal activity
Remarks: Numerous hydrothermal explosions, geysers, geothermal activity; currently restless, shown by seismically and ground deformation 2
From: U. S. National Park Service Web site, Geology Field notes - Yellowstone National Park, April 2000
At the heart of Yellowstone's past, present, and future lies volcanism. Catastrophic eruptions occurred here about 2 million years ago, then 1.2 million years ago, and then 600,000 years a go. The latest eruption spewed out nearly 240 cubic miles of debris. What is now the park's central portion then colla psed, forming a 28- by 47- mile caldera (or basin). The magmatic heat powering those eruptions still powers the park's famous geysers, hot sprin gs, fumaroles, and mud p ots. The spectacular Grand Canyon of the Yellowstone River provides a glimpse of Earth's interior: its waterfalls highlight the boundaries of lava flows and thermal areas. Rugged mountains flank the park's volcanic plateau, rewarding both eye and spirit.
From: Brantley, 1994, Volcanoes of the United States : USGS General Interest Publication
Y ellowstone Caldera is one of the largest and most active calderas in the world. The spectacular geysers, boiling hot springs, and mud pots that have m ade Yellowstone famous -- and even the strikingly be autiful Grand Canyon of Yell owstone through which the Yellowstone River plunges -- owe their existence to the trem endous volcanic forces that have affected the region during the past 2 million years. Cataclysmic eruptions 2.0, 1.3, and 0.6 million years ago ejected huge vo lumes of rhyolite magma; each eruption formed a caldera and extensive layers of thick pyroclastic-flow deposits. The youngest c aldera is an elliptical depression, nearly 80 kilomet ers long and 50 kilometers wide, that occupies much of Yellowst one National Park. The caldera is buried by seve ral extensive rhyolite lava flows erupted between 75,000 and 150,000 years ago.
T he Earth's crust beneath Yellowstone National Park is still restless. Precise surveys have detected an area in the center of the caldera that rose by as much as 86 centimeters between 1923 and 1984 and then subside d slightly between 1985 and 1989. Scientists do not know the cause of these ups and downs but hypothesize that they are related to the addition or withdrawal of magma beneath the caldera, or to the changing pressure of the hot g round water system above Yellowstone's large magma reservoir. Also, Yello wstone National Park and the area immediately west of the Park are historically among the most seismica lly active areas in the Rocky Mountains. Small-m agnitude earthquakes are common beneath the entire ca ldera, but most are located along the Hebgen Lake fault zone that extends into the no rthwest part of the caldera. A magnitude 7.5 earthquake occu rred along this zone in 1959 [Map,20K,InlineGIF] .
From: Newhall and Dzurisin, 1988, Historical Unrest at Large Calder as in the World: USGS Bulletin 1855
The Yellowstone region has produced three caldera-forming erupt ions in the past 2 mill ion y ears, two of those among the largest eruptions known to have occurred on Earth (each more than 1,000 cubic kilometers). Yellowstone's hydr othermal system is among the largest and most active in the world, and its historical seismicity and uplift are comparable to those at the most active calderas ...
Yellowstone Plateau
From: Wood and Kienle, 1990, Volcanoes of North America: United States and Canada: Cambridge University Press, 354p., p.263-267, Contribution by R. L. Christiansen
The Yellowstone Plateau spans the continental divide between the Northern and Middle Rocky Mountains, at an average elevation of around 2,400 meters. The plateau lies at the center of one of the Earth's largest volcanic fields, entirely post-dating 2.5 million years ago. The major eruptions of the volcanic field were exceedingly voluminous, but their products are only surficial expressions of the emplacement of a batholithic volume of rhyolitic magma to high crustal levels in several episodes. The total volume of magma erupted from the Yellowstone Plateau volcanic field since 2.5 million years ago probably approaches 6,000 cubic kilometers.
This great magmatic volume and the enormous calderas produced by the largest pyroclastic eruptions are associated with a surprisingly subtle morphology. The Yellowstone caldera, the youngest of three nested and overlapping calderas, is filled by younger rhyolitic lavas, and is readily recognizable in only one or two sectors. The two older, nested calderas, however, form part of a conspicuous circular basin at the west edge of the volcanic field, called Island Park which is enclosed along its eastern margin by a
Snake River Plain - Yellowstone Volcanic Province
From: Wood and Kienle, 1990, Volcanoes of North America: United States and Canada: Cambridge University Press, 354p., p.149-150, Contribution by Charles A. Wood.
An 80-kilometer-wide swath of basaltic and rhyolitic volcanism cuts across southeast Idaho for 450 kilometers. This Snake River Plain-Yellowstone (SRPY) volcanic province is the most dynamic area of volcanism in North America. This is not because of abundant historic eruptions -- there have been none -- but rather because of its rapid motion. SRPY is propagating to the northeast at 3.5 centimeters per year (Armstrong, et.al., 1975); it will slice through Montana and be at the Canadian border in approximately 20 million years. If past activity is a guide, SRPY doesn't simply cover terrain with volcanic rocks, but rather the pre-existing ground subsides up to 6 kilometers (Braile, et.al., 1982) between major faults (Sparlin, et.al., 1982) and is further churned up by the transit of magma and the formation of magma chambers. SRPY is a geologic roto-tiller.
According to the radiometric dating of Armstrong, et.al. (1975), SRPY activity began approximately 15 million years ago with silicic volcanism in southern Idaho. A series of now buried rhyolitic calderas formed in a northeast progression, with abundant basaltic volcanism lagging behind by 2-5 million years. Island Park and the two Yellowstone calderas are the most recent manifestations of the silicic volcanism, and Island Park is now being colonized by the basaltic wave of magma. ...
Yellowstone Hydrothermal Systems
From: Wood and Kienle, 1990, Volcanoes of North America: United States and Canada: Cambridge University Press, 354p., p.263-267, Contribution by R. L. Christiansen
The Yellowstone caldera region hosts the world's largest know hydrothermal system, highlighted by numerous geysers. This hydrothermal system accounts for an average heat flow from the caldera area 40 times greater than the global average. Although the latest eruptions were approximately 70,000 years ago, the immense hydrothermal system and a variety of geophysical characteristics indicate that magma still underlies the Yellowstone caldera at a shallow depth. A large negative gravity anomaly, low magnetic intensity, high electrical conductivity, shallow swarm seismicity, and large delays and high attenuation of seismic waves are all consistent with this inference.
Yellowstone is the oldest national park in the world and one of the leading tourest attractions in North America. U.S. Highways 16, 212, and 289 go through the Park. Many hydrothermal and volcanic features are marked.
Yellowstone "Hot Spot"
From: Dzurisin, Christiansen, and Pierce, 1995, Yellowstone: Restless Volcanic Giant: VOLCANO HAZARDS FACT SHEET: USGS Open-File Report 95-59
Scientists have traced Yellowstone's origin to a hot spot in the mantle, one of a few dozen such hot spots on Earth. Buoyant material from a hot spot rises through the upper mantle, bringing heat from the Earth's interior closer to the surface. The Yellowstone hot spot impinges on the base of the North American plate, one of several rigid plates that make up the Earth's crust. These plates move a few inches per year with respect to the stationary hot spots and each other, sometimes causing great earthquakes as the plates collide, grind past one another, or split apart.
From: Newhall and Dzurisin, 1988, Historical Unrest at Large Calderas in the World: USGS Bulletin 1855
Yellowstone lies at the intersection of the Basin and Range tectonic province, dominated by E-W extension, and the eastern Snake River Plain, a linear downwarp or graben that has been a locus for basaltic volcanism since middle Miocene time. According to one popular model, the rhyolitic Yellowstone Plateau marks the current location of a "hotspot" or melting anomaly in the upper mantle, and the basaltic Snake River Plain records the hotspot's northeastward track across the mobile North American Plate. ...
From: Kious and Tilling, 1996, This Dynamic Earth: The Story of Plate Tectonics: USGS Special Interest Publication
A few hotspots are thought to exist below the North American Plate. Perhaps the best known is the hotspot presumed to exist under the continental crust in the region of Yellowstone National Park in northwestern Wyoming. Here are several calderas (large craters formed by the ground collapse accompanying explosive volcanism) that were produced by three gigantic eruptions during the past two million years, the most recent of which occurred about 600,000 years ago. Ash deposits from these powerful eruptions have been mapped as far away as Iowa, Missouri, Texas, and even northern Mexico. The thermal energy of the presumed Yellowstone hotspot fuels more than 10,000 hot pools and springs, geysers (like Old Faithful), and bubbling mudpots (pools of boiling mud). A large body of magma, capped by a hydrothermal system (a zone of pressurized steam and hot water), still exists beneath the caldera. Recent surveys demonstrate that parts of the Yellowstone region rise and fall by as much as 1 cm each year, indicating the area is still geologically restless. However, these measurable ground movements, which most likely reflect hydrothermal pressure changes, do not necessarily signal renewed volcanic activity in the area.
From: Newhall and Daniel Dzurisin, 1988, Historical Unrest at Large Calderas of the World: U. S. Geological Survey Bulletin 1855
Yellowstone lies at the intersection of the Basin and Range tectonic province, dominated by E-W extension, and the eastern Snake River Plain, a linear downwarp or graben that has been a locus for basaltic volcanism since middle Miocene time. According to one popular model, the rhyolitic Yellowstone Plateau marks the current location of a "hotspot" or melting anomaly in the upper mantle, and the basaltic Snake River Plain records the hotspot's northeastward track across the mobile North American Plate.
Focal mechanisms of a magnitude 7.5 earthquake and its aftershocks (Hebgen Lake, 1959) suggested N-S extension near Hebgen Lake (about 70 kilometers northwest of Yellowstone) and radial compression near the caldera. Focal mechanisms of more recent earthquakes and geologic mapping in the caldera suggest dominant ENE-WSW or E-W extension.
Three times in the past 2 million years, large reservoirs of rhyolite magma have accumulated in the upper crust at Yellowstone, triggering cataclysmic eruptions and caldera collapses 2.0, 1.3, and 0.6 million years ago. The first great eruption (2.0 million years B.P.) produced the Huckleberry Ridge Tuff (more than 2,450 cubic kilometers) and a composite caldera more than 75 kilometers long, extending from Island Park on the west to central Yellowstone Park on the east. The second eruption (1.3 m.y. B.P.) produced the Mesa Falls Tuff (more than 280 cubic kilometers) and the Island Park Caldera west of Yellowstone Park; the third (0.6 m.y. B.P.) produced the Lava Creek Tuff (more than 1,000 cubic kilometers) and the present Yellowstone Caldera. Rhyolitic volcanism resumed within the Yellowstone Caldera after structural resurgence formed the Sour Creek and Mallard Lake resurgent domes. Renewed doming in the western caldera culminated with extrusion of 1,000 cubic kilometers of intracaldera rhyolite flows between 150,000 and 75,000 years ago.
There is abundant geophysical evidence for residual partial melt beneath Yellowstone Caldera, and the consensus among those who have studied the area is that the Yellowstone magmatic system will likely erupt again.
Deformed terraces along the shore of Yellowstone Lake and the Yellowstone River record a complex history of Holocene deformation that has continued to the present. Based on studies of the terraces, Hamilton (1985) proposed that intracaldera subsidence totaling more than 80 meters occurred in stages during the early Holocene, and Meyer and Locke (1986) inferred net uplift of about 10 meters in the northern Yellowstone Lake area during the late Holocene. The latter authors also cited geomorphic evidence that during the past several thousand years the lake fell to a level near the present, rose 6-7 meters, fell to the present level or below, and now is rising again to differential uplift of its outlet.
Yellowstone Caldera currently contains one of the largest and most active hydrothermal systems in the world, and hydrothermal activity probably has been relatively constant for at least the past 10,000 years. The contemporary heat output of the Yellowstone magmatic system is 4 x 10^16 cal/yr, or 5,500 MW
From: Wood and Kienle, 1990, Volcanoes of North America: United States and Canada: Cambridge University Press, 354p., p.263-267, Contribution by R.L.Christiansen
The Yellowstone Plateau spans the continental divide between the Northern and Middle Rocky Mountains, at an average elevation of around 2,400 meters. The plateau lies at the center of one of the Earth's largest volcanic fields, entirely post-dating 2.5 million years ago. The major eruptions of the volcanic field were exceedingly voluminous, but their products are only surficial expressions of the emplacement of a batholithic volume of rhyolitic magma to high crustal levels in several episodes. The total volume of magma erupted from the Yellowstone Plateau volcanic field since 2.5 million years ago probably approaches 6,000 cubic kilometers.
This great magmatic volume and the enormous calderas produced by the largest pyroclastic eruptions are associated with a surprisingly subtle morphology. The Yellowstone caldera, the youngest of three nested and overlapping calderas, is filled by younger rhyolitic lavas, and is readily recognizable in only one or two sectors. The two older, nested calderas, however, form part of a conspicuous circular basin at the west edge of the volcanic field, called Island Park which is enclosed along its eastern margin by a younger constructional lava platform at the west edge of the Yellowstone Plateau.
The Yellowstone Plateau volcanic field erupted a bimodal assemblage of basalt and rhyolite in three cycles of activity. Each cycle began with eruptions of both basalt and rhyolite; with time, the largest volume of rhyolite vented as lavas from developing ring-fracture systems. The climax of each cycle was marked by extremely rapid and voluminous eruptions of rhyolitic magma as ash flows from the ring-fracture system -- hundreds to thousands of cubic kilometers being ejected in a few hours or days -- and by collapse of the source area to form a large caldera. Post-collapse volcanism in each caldera has tended to fill it with rhyolitic lavas. Throughout each cycle of mainly rhyolitic volcanism, both basaltic and some rhyolitic lavas continued to erupt on the margins of the volcanic field, but no basalts erupted within the major active rhyolitic source areas.
The ash flows erupted at the climax of each cycle form the three largely welded cooling units of the Yellowstone group, providing a framework for the stratigraphy of the volcanic field. The 2,500-cubic-kilometer Huckleberry Ridge Tuff erupted at 2 million years ago, the 280-cubic-kilometer Mesa Falls Tuff at 1.3 million years ago, and the 1,000-cubic-kilometer Lava Creek Tuff at 0.6 million years ago. Each of these great eruptions produced fallout ash deposits over large parts of the western United States, leaving recognizable remnants as far east as the Mississippi River. The first and third cycles were sustained by enormous bodies of rhyolitic magma that accumulated to batholithic size, the highest parts of each intruding and deforming its roof to form compound ring-fracture zones. When a major eruption began from one of these high-level portions of the batholithic chamber, the violent degassing triggered contemporaneous or successive eruptions from the adjacent or overlapping ring-fracture zones, producing composite ash-flow sheets and compound calderas that embrace the cluster of ring-fracture zones.
The compound caldera that formed during the climactic first-cycle Huckleberry Ridge eruption -- largest of the three -- spanned at least 80 kilometers from Island Park (at the margin of the basalt-covered Snake River Plain, west of Yellowstone National Park), past the northern Teton Range and Jackson Hole on the south, to the center of the Yellowstone Plateau. The second-cycle Henrys Fork caldera is the smallest of the three, approximately 20 kilometers; both it and the surface outcrop of the Mesa Falls Tuff are restricted to the Island Park area. The third cycle began with the eruption of a series of voluminous rhyolitic lavas from all sectors of a growing fracture system that embraced two adjacent ring-fracture zones. The compound third-cycle Yellowstone caldera, related to the Lava Creek Tuff eruption, is 70 x 40 kilometers across in the center of the Yellowstone Plateau. The caldera is resurgent, with an early post-collapse dome uplifted within each of its two segments, followed by emplacement of early post-resurgence rhyolitic lavas from the enclosing ring-fracture zones.
Renewed magmatic activity has produced voluminous lavas in the Yellowstone caldera since approximately 150 thousand years ago, perhaps even indicating a fourth volcanic cycle. Following emplacement of a large rhyolitic lava flow int he western ring-fracture zone, renewed uplift of the resurgent dome occurred, reflecting insurgence of magma into the caldera system. Since that time, voluminous rhyolitic lavas (several individual flows exceeding 50 cubic kilometers) have filled the central part of the caldera and overflowed its western rim. These lavas were emplaced in three major episodes at approximately 150 thousand years ago, 110 thousand years ago, and 70 thousand years ago, each time erupting from both the western and eastern sides of the western ring-fracture zone to form the Madison and Central plateaus, respectively. The aggregate volume of these lavas is approximately 1,000 cubic kilometers. Deformation, probably related to continued magmatic activity beneath the Yellowstone caldera, continues with caldera-wide uplift and subsidence at rates as high as 2 centimeters per year. ...
The Yellowstone caldera region hosts the world's largest know hydrothermal system, highlighted by numerous geysers. This hydrothermal system accounts for an average heat flow from the caldera area 40 times greater than the global average. Although the latest eruptions were approximately 70,000 years ago, the immense hydrothermal system and a variety of geophysical characteristics indicate that magma still underlies the Yellowstone caldera at a shallow depth. A large negative gravity anomaly, low magnetic intensity, high electrical conductivity, shallow swarm seismicity, and large delays and high attenuation of seismic waves are all consistent with this inference.
|
Y