Abstract Climate warming and degradation of glaciers and permafrost in High Mountain Asia is threatening the sustainability of the region’s natural ‘water towers’ and allied ecosystems and infrastructure. Approximately 25,000 Himalayan rock glaciers exist and, being more resilient to climatic change than glaciers, they represent important freshwater reservoirs. Yet these rock glaciers’ ice content remains poorly quantified. Here, using Interferometric Synthetic Aperture Radar to track surface movement and Ground‐Penetrating Radar (GPR) to quantify buried ice, we present the first direct measurements of ice within the active Gokyo Rock Glacier, situated above 4700 m, in central Nepal (27.9416°N, 86.6920°E). Our unique data show surface movement up to 1 m a−1, consistent with active rock glaciers elsewhere, while geophysical interpretation reveals two buried massive ice bodies up to 28.0 (±2.1) m thick, totaling an estimated freshwater volume of 5.23−0.81+0.88 ${5.23}_{-0.81}^{+0.88}$ × 105 m3. These findings emphasize rock glaciers represent important, slowly released freshwater reserves as regional warming accelerates.