What is the geologic description of the Valles Caldera?
The Valles Caldera is a collapsed volcanic crater formed by a massive eruption that occurred 1.2 million years ago. The eruption expelled about 65 cubic miles of magma in the form of ash, pumice, and gas. After the eruption occurred, the empty chamber that had held the magma could no longer support the earth above it. Consequently, the earth collapsed, forming a giant crater, or caldera, approximately 12 miles in diameter. The first massive caldera in the Jemez was formed by an eruption 1.6 million years ago (the Toledo Caldera), which was mostly destroyed by the eruption that formed the Valles Caldera 400,000 years later.
