Tidewater glacier cycle

Climate change causes a shift in the equilibrium line altitude (ELA) of a glacier.

This altitude shift, in turn, prompts a retreat or advance of the terminus toward a new steady-state position.

[9] This effect contributes to the insensitivity of a glacier to climate when its terminus is either retreating or advancing in deep water.

Pelto and Warren (1991) found a similar calving relationship with tidewater glaciers observed over longer time periods, with slightly reduced calving rate to the mainly summer rates noted by Brown et al.

[11] By using accumulation area ratio (AAR) data for Alaskan tidewater calving glaciers, Pelto (1987)[11] and Viens (1995)[12] produced models showing that climate acts as a first-order control on the advance/retreat cycle of calving glaciers during most of the advance retreat cycle, but there are climate insensitive periods as well.

As the advance proceeds the terminus shoal will be pushed in front of the glacier and continue to build, keeping the calving rate low.

The glacier is not very sensitive to climate during the advance as its AAR is quite high, when the terminus shoal is limiting calving.

Brady Glacier has been thinning during the last two decades due to the higher equilibrium line altitudes accompanying warmer conditions in the region, and its secondary termini have begun to retreat.

This allowed the prediction in 1980, by the United States Geological Survey (USGS), of the retreat of the Columbia Glacier from its terminus shoal.

The USGS was monitoring the glacier due to its proximity to Valdez, Alaska, the port for crude oil export from the Alaskan Pipeline.

[2] Based on the recent thinning it is suggested that Brady Glacier is poised to begin retreat.

However, in the case of San Rafael Glacier, Chile, a switch from retreat (1945–1990) to advance (1990–1997) was noted.

The best current example is illustrated by the United States Geological Survey study of Columbia Glacier.

The glacier flow, i.e., the movement of the ice toward the sea, also increased, it was inadequate to keep pace with the break-up and expulsion of icebergs.

The water remains deep and the calving rate and glacier velocity very high, indicating retreat will continue.

At this point, just like having a balloon payment in an adjustable rate mortgage, the glacier has to pay a whole new portion of its balance via icebergs.

The entrance of the bay was filled by a tidewater glacier face that calved icebergs directly into the Gulf of Alaska.

A century later glacier retreat has opened a multi-armed bay more than 30 miles long.

The glacier calving front experienced a major retreat of 8.5 km in those 25 years as a result of rapid thinning [1].

Le Conte Glacier currently has an AAR of 90, is at a retracted position and seems likely to be set to advance after building a terminus shoal.

By the time John Muir saw the glacier in 1890, it was near its minimum extent, at a location where the fjord narrowed, with deep water in front.

[15] From 1986 to 2005, the equilibrium line altitude on the glacier rose without a significant terminus shift causing the AAR to decline to about 72.

Pelto and Miller concluded that the current reduction in rate of advance is since 1970 is attributable to the laterally expanding terminal lobe as opposed to declining mass balance and that the primary force behind the Taku Glacier's advance since about 1900 is due to positive mass balance.

[15] The recent lack of positive mass balance will eventually slow the retreat if it persists.

A tidewater glacier is not sensitive to climate during the advancing and drastically retreating phases of its cycle.