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Glaciologists track glacier health using a mix of satellite imagery, ground-based GPS stakes, and ice cores drilled to reveal decades of snowfall layers. Satellites measure surface elevation changes over vast areas, but cannot detect what happens deep within the ice, so researchers still travel to remote glaciers to install stakes that record melting rates directly. These measurements have shown that most monitored glaciers worldwide are losing mass, though a small number in high-altitude regions with increased snowfall have thickened slightly. Long-term monitoring is complicated by funding gaps, as maintaining remote field stations in polar and mountain regions is costly, and some historical monitoring sites have been abandoned entirely, creating gaps in decades-long data records that scientists say are difficult to fill retroactively.