Geologic study of the deposits found exposed in these trenches and minerals found in fault zones will provide evidence of how frequently and how much faults have moved in the past. Geologists will use dozens of trenches to investigate past movement of faults. The information will be used as part of the seismic hazard analysis of Yucca Mountain. Calderas form when large volumes of magma erupt rapidly. This removes the underground support for the volcano, and surface collapses and forms a circular depression, or caldera.
Calderas can range in size from the few miles to tens of miles across.
The caldera complex, which was the source of Yucca Mountain's welded tuffs, is about 20 miles across and centered about 17 miles north of the mountain. The massive volcano that formed Yucca Mountain is long extinct, but scientists are studying seven small and long inactive volcanoes in the Yucca Mountain area. They want to determine if one might erupt in the next 10,000 years and if an eruption might affect an underground nuclear repository. By studying layers of soil and rock to learn about past volcanic activities, scientists have been able to make predictions about the future. The probability of a future volcanic eruption directly intersecting a repository at Yucca Mountain is estimated to be about one in 70,000,000 per year, as confirmed by an independent panel of experts.