Yellowstone National Park as we know it today was created through countless volcanic activity on the Yellowstone hot spot, starting with rhyolitic ash and lava eruptions within the Owyhee highlands over the past two million years in the Late Pliocene era. It all began 16 million years ago, with the movement of the North American Plate over an active volcanic source that generated the Owyhee-McDermitt, Bruneau-Jarbidge, Magic Reservoir, and the Heise volcanic fields. It finally culminated in the Island Park-Yellowstone center in Wyoming. The McDermitt Caldera, lying in the southeast corner of Oregon, is considered the starting point for the Yellowstone hot spot.
The most noticeable alteration that formed is the Yellowstone Plateau Volcanic Field, which arose from the Island Park Volcanic Center at the northeast margin of the Snake River Plain.
View of the Yellowstone Caldera
This volcanic plateau has formed through three different cycles that eventually formed a caldera (a basin-shaped volcanic depression) in the west part of Yellowstone that caused a spread of pyroclastic materials to flow over vast areas. After all of this material, including ash, pumice, and other fragments, accumulated into one area, it formed hard lava-like rock. These ash-flow sheets account for more than half of the material that erupted from Yellowstone, which include the Huckleberry Ridge, Mesa Falls, and Lava Creek Tuffs (USGS).
1. A large area was uplifted from a development and rise of rhyolite that formed the magma chamber in the Earth’s crust. This stretching due to the uplift leaded to radial fracturing and faulting in addition to lava flows.
2. The rhyolite magma reached a point of over-pressurization and erupted through the fracture zone where the large area was uplifted, and produced ash-flow sheets. The top of the magma chambers collapsed as the chamber was partly emptied, producing a caldera.
3. After the volcano has collapsed and the caldera has formed, smaller eruptions occured as well as more rhyolite lava flows. In this third stage, although it occurred in the other two stages as well, hydrothermal activity is the main factor on the surface of the magma.
The different types of volcanic material in the Yellowstone National Park region resulted in these rock formations, also referred to as “tuffs.” They are the Huckleberry Ridge tuff, the Lava Creek tuff, and the Mesa Falls tuff.
Today, lakes formed in the caldera after rivers leading into the caldera were blocked by the flows, creating a dam. A good deal of the eastern boundary of the caldera is buried under the Yellowstone Plateau, with a southwest section along Bishop Mountain as Big Bend Ridge (Geology of the Pacific Northwest).
Undine Falls in Yellowstone National Park flows over areas of basalt lava
The most recent eruptions occurred 160,000 to 70,000 years ago. They extruded thick rhyolite lava flows in the youngest caldera, as well as basalt lava flows around the margins. It is likely that more volcanic activity will occur in the future at Yellowstone due to the “long-term nature of volcanism” in the area (USGS). Another caldera would most likely not form, but ryholite or basalt lava flows would occur with some explosive activity.