EVIDENCE FOR INFLATION AND DEFLATION IN LAVAS FLOWS WEST OF MITER CRATER, ICE SPRINGS VOLCANIC FIELD, BLACK ROCK DESERT, UTAH

Ice Springs Volcanic Field represents the youngest monogenetic volcanism (~660 yrs old; Valestro et al. 1972) in west-central Utah’s Black Rock Desert. Ice Springs exhibits a distinct cinder cone complex and related basalt lava flows. Detailed mapping and topographic profiling of the pahoehoe flows west of Miter Crater reveal a history of flow inflation and deflation processes. Using Differential Global Positioning System (DGPS) data, we created five topographic profiles across the lava flows with cm-scale accuracy (horizontal and vertical). Each profile shows up to three elevation terraces, interpreted to be inflated sheet lobes, inflation plateaus, or deflation surfaces in the lava flows.

DGPS data reveal a gentle slope to the south, from elevations of 1445.5 masl in the north to 1435.0 masl in the south. Several inflated sheet lobes that mark the northern extent of the profile are up to 5 m higher than the surrounding topography. The central region exhibits an inflation plateau of generally consistent elevation, except for a series of 2 m high pressure ridges. The plateau has prominent fractures near its margin. In contrast to this central inflation plateau is the southern region that displays the lowest topography, which we interpret to be a result of lava flow deflation. Nearly vertical walls bound this deflated area, which has an average basal elevation that is equal to the elevation of the depth of the nearby inflation plateau fractures. The stratigraphy of the walls show patterns in vesicularity and jointing consistent with inflation: a massive, jointed core that transitions upward into subhorizontal vesicle sheets and zones. Vesicle casts on the underside of vesicular flow units are interpreted as evidence of inflation, formed by lava injection beneath a solidified flow unit. In many areas, the bottom two-thirds of the walls have a pasty lava coating with near-vertical grooves. Within the deflated area, the most pronounced morphology is a series of distinct pillars, typically 5 m higher than the surrounding topography and at similar elevations (within 1.5 m) to the central region’s inflation plateau. In addition to these pillars, there are numerous topographically smaller tumuli (up to 2 m in height) that are parallel or slightly oblique to the inflation plateau walls, with a 0.59 tumuli-to-wall height ratio.