A NEW LOOK AT EXTENSION AND VOLCANISM AT CRATERS OF THE MOON NATIONAL MONUMENT AND PRESERVE, IDAHO

Craters of the Moon National Monument and Preserve (CRMO) showcases some of the best examples of intracontinental basaltic volcanism found in the United States. CRMO is located on the eastern Snake River Plain (ESRP) in south-central Idaho and contains almost all of the Great Rift, which is the best developed volcanic rift zone on the ESRP. The Great Rift extends for 85 km across the ESRP, and runs generally in a NW-SE direction. The ESRP contains several other volcanic rift zones that also parallel range fronts associated with Basin and Range extension. These rift zones appear to accommodate extension by injection of dikes. The object of our ongoing study is to evaluate the relative timing and abundance of volcanic activity and rift-related fracturing of the upper crust.

The Great Rift has extensional fabric characteristic of the Basin and Range Province and lies along the Yellowstone hotspot track that extends from the Oregon/Idaho/Nevada junction to the Yellowstone Plateau. Volcanic activity along the Great Rift is concentrated in the north, at the edge of the ESRP, where the Great Rift impinges on the Pioneer Mountains. Large fissures in the southern part of the developed area of CRMO are predominantly non-eruptive and cut volcanic rocks that are approximately 2,200 years old. To the north, in the most visited part of the monument, the width and length of fissures generally decreases and there is abundant evidence for volcanic activity in the form of spatter ramparts and proximal, shelly pahoehoe sheet flows with abundant tree molds.

A study of aerial photographs and detailed field mapping of both eruptive and non-eruptive fissures will generate a new large-scale map of approximately 10 miles of the northern end of the Great Rift. The map will aid comparisons to the East Rift Zone of Hawaii's Kilauea volcano and Iceland's Hekla volcano, will elucidate the relationship between extension and volcanism at CRMO, and will help to predict future volcanic activity by interpreting the nature and relative timing of volcanic and tectonic events in the northern part of the rift.