Last update: December 13th, 2019 at 8:00 am
Of the approximate 200,000 glaciers on Earth, about 1 percent of them are classified as “surging.” Most glaciers flow at a fairly steady rate, but surging glaciers lurch forward in bursts, in some cases flowing 10 to 100 times faster than normal for short episodes. Though it varies by individual glacier, surges usually last less than a year and occur every 15 to 100 years, according to the National Snow & Ice Data Center.
If you can get to a glacier’s terminus, surging is easy enough to identify. In fact, it was so obvious at Black Rapids Glacier in Alaska in 1937 that it inspired headlines such as ”Runaway Glacier” and “Glacier Develops Wanderlust.” But most glaciers are so remote and difficult to reach that monitoring surges from the ground poses serious logistical challenges.
However, surging glaciers do leave telltale clues that are detectable from the air and from space. One important clue that a glacier is surging: its surface will contain distinctive curved lines called looped medial moraines. Medial moraines are ridges of debris that form in the middle of an ice flow when ice from two glaciers merge. Non-surging glaciers contain medial moraines as well, but they are generally straight. It’s when a surging glacier encounters a slower-moving glacier that spectacular loops, bends, and kinks develop.
Bivachny Glacier, a surging glacier in Tajikistan, contains a textbook example of looped medial moraines. Notice in this photograph taken from the International Space Station how the fairly straight moraines of Bivachny begin to warp as they encounter ice from MGU glacier. The snaking pattern downstream of the junction of the two glaciers offers a record of the ongoing push-and-pull taking place. When Bivachy is not surging, MGU glacier pushes forward, partly blocking off Bivachny’s flow. As ice backs up and pressure builds, Bivachny eventually surges forward and pushes MGU’s dam back. When Bivachny’s surge slows down, MGU creeps back and the cycle starts anew. Based on field work and studies of satellite imagery, scientists believe that Bivachny has gone through at least three distinct surges in the second half of the 20th Century.
While Bivachny is the only surging glacier in the Fedchenko glacier system, it is one of about 60 surging glaciers in the Pamir Mountains. Other parts of the world with surging glaciers include Alaska, Iceland, the Yukon Territory, the central Andes, central Asia, and Greenland.