The tidewater glacier cycle is the idea that a glacier can facilitate its own advance by building a submarine shoal at its terminus, providing a buttress against calving and melting by warm ocean water. This advance is currently occurring in several places in Alaska, but one of the most dramatic examples is at Taku Glacier, where the advance process occurs today. For example, see the images below, which show the terminus position of Taku in 1933 versus today.
Taku is particularly dramatic, since it’s switched from calving to terminating on land. However, because it terminates on land, its extent is subject to the same limitations as any other land terminating glacier. But glaciers are incredibly erosive (which is why they can advance like this in the first place), so what happens when they can’t advance any more, but continue to push the sediment in front of them? My modelling work addresses this question, and the answer it provides is best illustrated with the following video.
The large retreat evident at the end of each advance is reminiscent of some of the catastrophic retreats that have been observed in Alaska recently. For example, Columbia Glacier has retreated nearly 20km in the last 25 years, and continues presently.
These kinds of events are important for a variety of reasons: changes in iceberg production can affect shipping (more icebergs=sad ships) and seals (more icebergs=happy seals), changes in freshwater inputs can affect fjord circulation, and shifts in the location and rate of sedimentation can influence whether fjord bottoms are viable habitat for benthic critters.