is located in north-central New Mexico in the central Jemez Mountains west of Santa Fe. It is the oldest of three young caldera-type volcanoes in the United States; the other two are Yellowstone in Wyoming and Long Valley in California. The Valles caldera-forming eruption occurred approximately 1.25 million years ago when huge volumes of Bandelier tuff
evacuated from a underground magma
storage region. As a result of the "supereruption," the ground subsided along a network of nearly circular faults, called a ring fracture
, leaving the caldera
, a 20 x 23 km (12 x 14 mi) depression. Resurgent doming
of the central caldera floor occurred between 1.25 and 1.22 million years ago, which was immediately followed by additional dome
eruptions around the caldera margins up until about 40,000 years ago. These resurgent and ring-fracture eruptions are interlayered with lake deposits, indicating the caldera has been at least partially filled by lakes since its formation. The youngest volcanism occurred in the southwest sector, which coincides with the present-day Valles geothermal system, which is fueled by a magma
storage region residing beneath the southwestern caldera.
A future Bandelier-Tuff
-forming eruption is highly unlikely. However, the chemical signature of the youngest Valles eruptive products is different from rocks erupted half a million years earlier, which may indicate changes in the magmatic system. The youngest eruptions were explosive and covered much of New Mexico in ash
. Roughly, about one eruption every 50,000 years has occurred at Valles, but the spacing between those eruptions is very irregular—it remains nearly impossible to predict whether such events will occur in the future.
New Mexico, Sandoval County
Most recent eruption:
40,000 years ago