Extremities:  Geology and Life in Yellowstone and Implications for Other Worlds


Yellowstone National Park includes the center of a large, recently active volcano - the Yellowstone Caldera complex. This page and the next show the major stages in the its history, based on Christiansen (2001) (U.S. Geological Survey). Caldera complex volcanos are common on Earth, and the Valles caldera complex volcano clearly shows their typical history. Yellowstone is also fairly typical, but its geology is difficult to see because:

  • The area was glaciated, which strongly modified the original volcanic topography.
  • The Yellowstone caldera was filled to overflowing intra-caldera lavas.
  • Yellowstone caldera is two overlapping simultaneous caldera complex volcanos, with two distinct ring fractures and two separate resurgent domes.
  • Yellowstone's lava flows are very difficult to distinguish from each other.

Yellowstone Area from Skylab
Valles with snow

Skylab image of the Yellowstone Park and surroundings looking north-east ('+' signs are from the camera). Yellowstone Lake is in the center, the Beartooth mountains are left of center, and the Bighorn mountains are the arc to the upper left. Bozeman is among the mountains to the lower left.
A Space Shuttle image of the Yellowstone area; north is at about 11:00 (counterclockwise from straight up). Wispy cirrus clouds cast shadows on the ground. The following images of the geology of the Yellowstone caldera volcano are annotated onto the center of this frame.
Pre-Caldera Rhyolites
Lava Creek Tuff

Pre-Caldera Eruptions Starting ~ 1.2 million years ago, volcanic activity shifted from the west to the site of Yellowstone Park with a series of obsidian (or rhyolite) domes and flows. These eruptions outlined the main ring fracture for the Yellowstone Caldera. These pre-caldera lavas are exposed rarely, the bright overlays, being mostly buried under younger rocks. The inferred original extents of these flows are in the pale overlays, with their inferred vents as stars. From Figure 8 and Plate 1 of Christiansen (2001). Other similar flows may not be exposed at all.
Lava Creek Tuff The major eruption at Yellowstone, 640,000 years ago, saw >300 cubic kilometers of volcanic ash erupted in just a few days or years. Much of this ash erupted as ash flows, 'slurries' of volcanic ash fragments in superheated steam and gas, which solidified to form the to form the Lava Creek ash-flow tuff. The Lava Creek looks just like the Huckleberry Ridge tuff. Outcrops of the Lava Creek are in the strong color overlays, and its inferred original distribution in the pale overlay. Loose ash from this eruption must lain thick on the whole area, as it spread over all of eastern North America (at least). From Plate 1 of Christiansen (2001).

Next - Yellowstone Caldera 2  |  To Valles Caldera 1  |  Back to Workshop
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