RECONSTRUCTION OF ERUPTION CONDITIONS BASED ON CRATER RIM STRATIGRAPHY AT MITER CRATER, ICE SPRINGS VOLCANIC FIELD, BLACK ROCK DESERT, UTAH

This study focuses on Miter Crater, the best-preserved cone of the Holocene, basaltic Ice Springs Volcanic Field, located in the Black Rock Desert, Utah. The primary objective is to construct a detailed eruptive history of late stages of the growth of Miter Crater by interpreting the volcanic stratigraphy on both the inside and outside walls of the cone. The study takes advantage of a newly excavated inward facing wall near the top of the crater rim that exposes an 8.3m high section of pyroclastics rocks. Methods include constructing several stratigraphic columns using both traditional measured section techniques and a laser range finder with DGPS system (cm-scale accuracy in the horizontal and vertical). Panoramic images of the inside and outside walls were also taken using Gigapan high-resolution photography.

The volcanic stratigraphy from the inside of Miter Crater reveals a sequence, from bottom to top, of welded spatter and large bombs (≤ 97 cm width, 30 cm height), welded spatter and small bombs (≤ 27 cm width, 16.5 cm height), ash lapilli, and a highly weathered layer of loose blocks and bombs. Approximately 100 individual bombs within the inner wall were identified and measured for their height (ranges from 32 to 5 cm), width (ranges from 97 to 11.5 cm), and approximate vesicularity (ranging from 5 - 30%). 4 samples were collected for detailed petrologic and vesicularity analyses. A Strombolian eruption style is inferred for this section.

A ~3 m thick roadcut outcrop on the outer flank of Miter Crater was also described and sampled to provide a more comprehensive sequence of eruptive activity. This outcrop is at a lower elevation but is stratigraphically above the inside outcrop. This section shows alternations in both grain size and degree of welding, suggesting changes in eruption intensity and style. 11 samples were collected, including fine and coarse lapilli, unconsolidated blocks and bombs, and intensely welded spatter. Two eruption styles are inferred during the last part of cone growth: Strombolian at the base and middle of the section, followed by Hawaiian fire fountaining with extreme welding at the top. Our analysis of pyroclast grain size and shape, aspect ratios, petrology will further contribute to understanding the overall history of Ice Springs Volcanic Field and style of volcanism during cone growth.