Divide the state total by the state inventory and the extrapolation starts to creak. Utah's 836 mapped rock glaciers [13] are credited with roughly 1 gigaton of water [16], and a gigaton of water is a cubic kilometer [17], so the mean feature would have to hold about 1.2 million cubic meters of ice [1]. Timpanogos, one of the largest in the state [5], holds 1.5 million [3]. The global number behaves the same way: 48 gigatons spread across 50,000 catalogued rock glaciers [15] comes to about 960,000 cubic meters each [3]. Either small rock glaciers are far icier than their footprints suggest, or the surface-area-to-volume rule, fitted using the Timpanogos result [14], is generous at the low end.
The measurement itself explains why nobody will settle that quickly. Bronson Cvijanovich made six trips to the ice above Emerald Lake in fall 2024, carrying a gravimeter to 232 stations on a 25-meter grid [7]. The instrument reads the density contrast between mountain rock and much lower-density ice, and gravitational acceleration drops further over thicker ice, according to geophysics professor Michael Thorne [8]. The readings then had to be corrected for the position of the sun and moon, terrain, latitude and elevation, after which months of computation produced a 3D image using Bayesian statistics [9]. Satellite imagery yields the outline and nothing about depth [10]. Inventory is cheap, volume is expensive, and that is the condition under which one calibrated site gets asked to speak for 50,000.
A number the summary does not give: if each of the 232 stations stands for a 25-meter cell, the survey covers about 145,000 square meters, which puts mean ice thickness near 10 meters [4] against the 37 meters that glaciology professor Leif Anderson describes under the rubble [6]. Most of the body is much thinner than the headline depth, whatever its shape.
The second study probably matters more than the volume. These are not Ice Age leftovers; they accumulated in the thousands of years after the Ice Age glaciers vanished [12], and the mass-gain model has rockfall burying persistent snow in the upper reaches [11]. The supply term for a rock glacier therefore includes rock delivery, not only snowfall and temperature, which is a different sensitivity from anything a snow course records.
For anyone doing water arithmetic in the arid West, the useful reading is narrow. 815,000 acre-feet [16] is a stock, and the work reported here gives no rate at which any of it reaches a stream. Describing the ice as unaccounted-for is fair [1]. Describing it as available would need a discharge measurement these campaigns did not make.
