ROCK CORRAL BUTTE, IDAHO: AN INFLATED FLOW FIELD IN THE EASTERN SNAKE RIVER PLAIN

Plains-style volcanism is common on Mars and Venus. The Martian and Venusian surfaces are covered with shield volcanoes, whose diversity of morphological expressions is still not fully understood. Being able to interpret the range of volcanic morphologies observed in plains-style volcanism will lead to a better understanding of eruption and emplacement styles, durations, and roles in magmatic volatiles on rocky planets.

Previous investigations of different shield volcanoes within the Eastern Snake River Plain (ESRP), Idaho, reveal a range of eruption and emplacement styles that can serve as an analog for the eruptive behaviors of small shields on Mars and Venus. Rock Corral Butte (RCB) is a 50,000-year-old basaltic shield volcano located at 43°22.25'N, 113°1.20'W in the ESRP. Its associated lava flow field displays mounds that are 2 to 4 m tall, 5 to 10 m long, and 3 to 10 m wide with flat or depressed interiors. These dimensions make them morphologically similar to Icelandic tumuli instead of stereotypical Hawaiian tumuli. Hawaiian tumuli are the result of repeated small batches of lava emplaced through preferred pathways within a growing lava flow field. In contrast, Icelandic tumuli, also called “flow-lobe tumuli,” are created through an increase in pressure from inside a cooling lava flow. This causes large areas of the solidified crust to be pushed upwards into domes that later deflate when the pressure exerted by the still-molten lava within the flow decreases. To constrain the emplacement style, rate, and duration of RCB’s lava flow field, we plan to examine the crystal-size distribution (CSD) of plagioclase and vesicle-size distribution (VSD) from samples. VSD and CSD can be obtained by examining samples collected from different distances and cardinal directions of the flow field from the vent. The VSD and CSD will be derived from the samples’ percent area of vesicles and plagioclase respectively. We will use photomicrographs of thin sections and Scanning Electron Microscope images of a subset of samples, combined with the freeware ImageJ, to quantify the abundance of vesicles and plagioclase along the flow length. These results will help us to evaluate cooling and degassing rates throughout the flow field, thus providing constraints on rates of emplacement and inflation.