Research: Crevasse fields

Can a water-filled crevasse reach the bottom surface of a glacier?  Materials engineer and glaciologist Johannes Weertman asked precisely this question in the early 1970s, and found that the answer was a resounding “Yes!” (as long as there is enough meltwater to keep driving it downward).  Crevasses that receive a lot of meltwater can, and regularly do, reach the bottom of glaciers, including the massive Greenland Ice Sheet.

 

Moulin formation, 2008
This crevasse, which formed in the bottom of a supraglacial lake, was filled with a massive amount of meltwater.  Thus, the crack here goes all the way to the bottom of the ice sheet, 1000 m below.

What is less certain is how typical it is for a crevasse to hydrofracture all the way to the bottom.  There are thousands of crevasse fields all across the Greenland Ice Sheet, and each crevasse field itself has hundreds of individual crevasses.  Some of them receive enough water to reach the bottom, but how many do not?  This is unknown.

Using a numeric model based in part on the work of Weertman on the elastic deformation of a water-filled crevasse, with additional components for creep closure and freezing of water inside the crevasse, we calculate the expected evolution of typical water-filled crevasses in crevasse fields across western Greenland.  We find that for the most part, crevasses can reach depths of a few hundred meters — NOT the bottom of the ice sheet — without healing (fully closing up or refreezing).

In the example below, meltwater drives a first-year crevasse to ~250 m depth over the summer, but all the water refreezes over the first winter, and the crevasse heals entirely.  In subsequent summers, the crevasse (if it reforms) will penetrate deeper because the ice is now warmer and cannot refreeze the water as rapidly.

21-Nov-2015_wGr_Crevolution
Results from the crevasse model, applied to a single crevasse in a hypothetical western Greenland crevasse field.  Only the first year is shown.  By healing fully in its first winter, the crevasse warms the ice, which allows deeper propagation in subsequent summers.

Interestingly, partially healed crevasses may host englacial water bodies (see panel e above) that can persist for years to decades as they slowly refreeze.  This might be a worthwhile component of the Greenland meltwater budget, or it may be a more trivial volume of water.

Crevasses forming on the Emmons Glacier, Mount Rainier, Washington, as the ice flows over bedrock bumps and deforms in response to those bumps.

Does this sound like an interesting research topic to you?

I’m always looking to add motivated students to my research group. I am particularly interested in working with students from minoritized backgrounds. If you’re interested in researching this topic, drop me a note and we’ll explore a research fit!