What is the term for the rapid advance of a glacier?

The term for the rapid advance of a glacier is a surge.

During a glacial surge, part of a glacier suddenly accelerates, sometimes moving up to 100 times faster than its normal flow for months or years. The extra movement transports a large mass of ice downhill and often pushes the glacier’s front forward, although not every surge produces a visible advance.

Surges are linked to changes beneath the ice, including the buildup of meltwater and reduced friction at the glacier bed. A glacier may remain relatively quiet for decades before entering an active surge phase. The quiet interval is called the quiescent phase, and surge cycles can range from roughly 15 to more than 100 years.

A surge is not the same as ordinary accumulation, which adds snow, or ablation, which removes ice through melting and evaporation. Calving describes ice breaking from a glacier’s edge, usually into water; it may accompany a surge but is not the name for the rapid advance itself.