#subalpine forest

Yellowstone National Park, WY (No. 23)

Yellowstone is at the northeastern end of the Snake River Plain, a great bow-shaped arc through the mountains that extends roughly 400 miles (640 km) from the park to the Idaho-Oregon border.

The volcanism of Yellowstone is believed to be linked to the somewhat older volcanism of the Snake River Plain. Yellowstone is thus the active part of a hotspot that has moved northeast over time. The origin of this hotspot volcanism is disputed. One theory holds that a mantle plume has caused the Yellowstone hotspot to migrate northeast, while another theory explains migrating hotspot volcanism as the result of the fragmentation and dynamics of the subducted Farallon Plate in Earth's interior.

The Yellowstone Caldera is the largest volcanic system in North America, and worldwide it is only rivaled by the Lake Toba Caldera on Sumatra. It has been termed a "supervolcano" because the caldera was formed by exceptionally large explosive eruptions. The magma chamber that lies under Yellowstone is estimated to be a single connected chamber, about 37 miles (60 km) long, 18 miles (29 km) wide, and 3 to 7 miles (4.8 to 11.3 km) deep. The current caldera was created by a cataclysmic eruption that occurred 640,000 years ago, which released more than 240 cu mi (1,000 km3) of ash, rock and pyroclastic materials.This eruption was more than 1,000 times larger than the 1980 eruption of Mount St. Helens. It produced a caldera nearly 5⁄8 mi (1.0 km) deep and 45 by 28 miles (72 by 45 km) in area and deposited the Lava Creek Tuff, a welded tuff geologic formation. The most violent known eruption, which occurred 2.1 million years ago, ejected 588 cu mi (2,450 km3) of volcanic material and created the rock formation known as the Huckleberry Ridge Tuff and the Island Park Caldera. A smaller eruption ejected 67 cu mi (280 km3) of material 1.3 million years ago, forming the Henry's Fork Caldera and depositing the Mesa Falls Tuff.

Yellowstone National Park, WY (No. 29)

Eruptions average 100 feet (31 m) high, with some rare “superbursts” of 200 feet (61 m) or more. Eruptions last 45-60 minutes in a series of bursts. Great Fountain Geyser takes 10-14 hours to rebuild to an eruption. The pool slowly fills, then begins to overflow 70-100 minutes before the eruption.

Like most geysers, Great Fountain Geyser experiences periods of irregularity. For the most part, it is dependable. While waiting for its display, watch for the eruptions of White Dome Geyser.

Lower Geyser Basin

The Lower Geyser Basin sits on unstable glacial gravel on top of solid rock. The jarring energy of an earthquake can make the gravel vibrate and shift position, and compact or fracture.

All these changes affect water supplies to hot springs. They might force muddy water to the surface, clouding existing pools or creating new ones. They might divert water from a pool, causing it to dry up. Water temperatures might also increase or decrease due to these subsurface changes.

In the days after the Hebgen Lake earthquake of 1959, all of these changes were observed in various springs of the Firehole River geyser basins. The epicenter (point of origin) of the quake was determined to be about 31 air miles (50 km) northwest of the Fountain Paint Pots area.

Yellowstone National Park, WY (No. 22)

As the name suggests, Wall Pool is a pool with a wall and an overhanging shelf of sinter to the west. Wall Pool is related to Black Opal Pool and Black Diamond Pool as a hydrothermal explosion crater. Wall Pool was created by one of the steam explosions in the early 1900s. Wall Pool exploded again in 2005, but activity has continued to decrease. It actively boils and the edges of the pool and surrounding runoff contain orange and yellow thermophiles.

Wall Pool has an average temperate of 190.5°F (88°C), an average pH of 7.9, and an average conductivity of 1833 uS/cm.

Yellowstone National Park, WY (No. 21)

Black Diamond Pool is a large murky blue pool with water flowing into other pools nearby. Soft sinter and sparse vegetation surrounds the area of the pool. Outflow from the pool forms braided channels of orange and green thermophiles. These large pools formed from hydrothermal explosions. While not all historic explosions are known, Black Diamond Pool erupted black murky water after an earthquake in July 2006, with several explosive eruptions in the following days. Eruptions continue to be infrequent since, with the last eruption observed in 2016.

Black Diamond Pool has an average temperate of 148.5°F (64.7°C), an average pH of 8.2, and an average conductivity of 2092 uS/cm.

Water

Yellowstone National Park, WY (No. 24)

Each of the three climactic eruptions released vast amounts of ash that blanketed much of central North America, falling many hundreds of miles away. The amount of ash and gases released into the atmosphere probably caused significant impacts on world weather patterns and led to the extinction of some species, primarily in North America.

A subsequent caldera-forming eruption occurred about 160,000 years ago. It formed the relatively small caldera that contains the West Thumb of Yellowstone Lake. Since the last supereruption, a series of smaller eruptive cycles between 640,000 and 70,000 years ago, has nearly filled in the Yellowstone Caldera with 80 different eruptions of rhyolitic lavas such as those that can be seen at Obsidian Cliffs and basaltic lavas which can be viewed at Sheepeater Cliff. Lava strata are most easily seen at the Grand Canyon of the Yellowstone, where the Yellowstone River continues to carve into the ancient lava flows. The canyon is a classic V-shaped valley, indicative of river-type erosion rather than erosion caused by glaciation.

Each eruption is part of an eruptive cycle that climaxes with the partial collapse of the roof of the volcano's partially emptied magma chamber. This creates a collapsed depression, called a caldera, and releases vast amounts of volcanic material, usually through fissures that ring the caldera. The time between the last three cataclysmic eruptions in the Yellowstone area has ranged from 600,000 to 800,000 years; however, the small number of such climactic eruptions cannot be used to make an accurate prediction for future volcanic events.