Costs of rapid sea level rise globally to infrastructure (houses, roads, and farms, etc.) is likely to be large. A possible source of water for sea level rise is the West Antarctic Ice Sheet, and Thwaites Glacier in particular. Ice sheets and glaciers contain vast quantities of water (in the form of ice) that is continually shed to the ocean, and continually replenished by snowfall (from water that evaporates from the oceans). If the amount of ice that Thwaites Glacier loses to the ocean over the next decades is much greater than the amount it receives as snowfall, then sea level in all the world's oceans would rise, possibly as much as a meter (approximately 3 feet). In order to estimate how likely such a catastrophic scenario would be, we need to better understand the surface over which Thwaites Glacier slides. If we can better characterize that layer ("is to smooth? Is it rough? Is it soft? Is it hard?"), then computer models of Thwaites would be much improved and we can make better projections of the amount of ice that Thwaites Glacier would shed to the ocean.