Tracing volcanic rocks in Yellowstone may help understand history

Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week’s contribution is from Natali Kragh, graduate student, and Madison Myers, assistant professor of Igneous Processes, both in the Department of Earth Sciences at Montana State University.

Geologic units of the Absaroka volcanic province in northeastern Yellowstone National Park show volcaniclastic sandstones grading up into a conglomerate, followed by another sequence of sandstone to conglomerate. These repeating layers of the same-looking material make it difficult to assign them to a specific volcanic group. 

Natali Kragh, Montana State University

Before Yellowstone was the volcano we know and love today, in its place, 50 million years ago, was a volcanic arc called the Absaroka volcanic province. This ancient arc, similar to the modern-day Cascade range, produced volcanic material that covers more than 23,000 square kilometers (almost 9,000 square miles). For reference, this is about the same size as the states of Vermont or New Hampshire.

Besides producing massive volcanic centers that still dot the landscape today (for example, Mount Washburn), erosion of the three main volcanic groups,

View Source