BALLISTIC ANALYSIS OF VOLCANIC EJECTA: ICE SPRINGS VOLCANIC FIELD, BLACK ROCK DESERT, UTAH

Ice Springs Volcanic Field, located in the Black Rock Desert west of Fillmore, Utah, is composed of three large craters, Crescent, Miter, and Terrace, and several smaller craters. Volcanism in the Black Rock Desert, positioned in the Basin and Range Province, results from east to west crustal extension, vertical crustal thinning, and high angle normal faults. Concern over the hazards of the volcanic field, ±660 years old, reactivating prompted the need for a hazards model. This study focuses on Miter Crater in order to conduct a ballistic analysis of the blocks and bombs observed along the crater rim. Data analysis of Miter Crater ejecta can then contribute toward a regional hazards model.

Thirty-four blocks and bombs were sampled along the rim of Miter Crater, recording the dimensions of the three major orthogonal axes of each specimen and the associated morphology and density. Geographic locations and altitudes were recorded for each block and bomb, as well as the eruptive center, using two GPS devices simultaneously to ensure accurate measurements. Teardrop, quot (cowpie), spheroidal, and ribbon bombs were identified and sampled around the crater rim. However, no bombs were found on the northeast side of Miter’s northern breach. Bombs were highly vesiculated and not found in-situ due to decades of quarrying. All blocks sampled were massive basalts and were found in-situ in the northeastern quadrant (the only undisturbed section of Miter Crater from quarrying). The crater rim was tracked following the inner crater rim, so it is a minimum estimate of the crater area. Tracking the crater rim accurately gives a quantitative degree of error when bombs and blocks are not in-situ, as they can be compared to the absolute topographic high, and could not have moved farther than that distance by natural movement. Data collected was then used to model possible trajectories and muzzle velocities for each block and bomb according to their respective sizes and positions along the Miter crater rim. A volcanic hazards map can be created from these results for Miter Crater, assuming the volcano still operates within similar parameters.