Contemporary Movement of Rock Glaciers in the La Sal and Uinta Mountains, Utah, USA

Rock glaciers are common landforms in mountainous areas of the western US. The motion of active rock glaciers is a key indicator of ice content, offering connections to climate and hydrologic systems. Here, we quantified the movement of six rock glaciers in the La Sal and Uinta Mountains of Utah through repeat differential GPS surveying. Networks of 10 to 41 points on each rock glacier were surveyed in September, 2021; July, 2022; September, 2022; and July, 2023. We found that all features are moving with average annual rates of motion from 1.5 ± 0.8 to 18.5 ± 7.5 cm/yr. Rock glaciers move up to 3x faster in the summer than in the winter, and rates of motion were greater in 2023 after a winter with above-average snowfall, emphasizing the role of liquid water availability. Velocities of individual points in the winter of 2021-22 are positively correlated with velocities during the winter of 2022-23, suggesting that spatial variability of motion is not stochastic, but rather reflects internal properties of each rock glacier. Bottom temperature of snow measurements during winter, and the temperature of springs discharging water in summer, suggest that these rock glaciers contain modern permafrost. Radiocarbon data document advance of one rock glacier during the Little Ice Age. Our GPS dataset reveals complicated patterns of rock glacier movement, and the network of survey points we established will be a valuable baseline for detecting future cryosphere change in these mountains.

岩冰川（rock glaciers）是美国西部山区常见的地貌类型。活动岩冰川的运动是其冰体含量的关键指示指标，可为气候与水文系统研究提供关联依据。本研究采用重复差分GPS（differential GPS）测量技术，对美国犹他州拉萨尔山脉与尤因塔山脉内的6处岩冰川的运动状态进行了定量分析。每处岩冰川布设了由10至41个监测点组成的观测网络，分别于2021年9月、2022年7月、2022年9月及2023年7月完成了复测。研究结果表明，所有岩冰川的年均运动速率介于1.5±0.8至18.5±7.5厘米/年之间。岩冰川夏季运动速率最高可达冬季的3倍；在降雪量高于气候均值的冬季过后，2023年的运动速率显著提升，这凸显了液态水可获得性的关键调控作用。2021-2022年冬季各监测点的运动速率与2022-2023年冬季的运动速率呈显著正相关，这表明岩冰川运动的空间变异并非随机现象，而是反映了每处岩冰川的固有内部属性。冬季积雪底部温度测量结果，以及夏季泉水出水温度测量结果均证实，这些岩冰川中赋存现代多年冻土（permafrost）。碳十四测年数据显示，有一处岩冰川在小冰期（Little Ice Age）期间发生过前进运动。本研究获取的GPS数据集揭示了岩冰川运动的复杂时空模式，我们布设的监测网络将成为监测该山区未来冰冻圈（cryosphere）变化的宝贵基准基线。