Glacial surges are short-lived events where the flow velocity on a portion of a glacier can increase up to 100 times faster than normal during a few months or years.
[6] The period of stagnation and build-up between two surges typically lasts 10 to 200 years and is called the quiescent phase.
[9][10] Features observed during the active or surge phase include potholes, known as lacunas[11] and medial moraines.
The distribution and pressure of water at the bed modulates the glacier's velocity and therefore mass balance.
[14] The evolution of the drainage system under the glacier plays a key role in surge cycles.
[citation needed] For example, poorly consolidated sedimentary rocks are more prone to failure under stress; a sub-glacial "landslip" may permit the glacier to slide.
Meier and Post[16] suggest that once mass accumulates to a critical point, basal melting begins to occur.