Galloping Glaciers

Galloping Glaciers

Normally the glaciers of the Earth are lethargic and show little change as they plod wearily at the imperceptible rate of one or two inches per day. Scientists are able to follow their progress and determine changes by an annual check of their position. It is not uncommon for glaciers to show little change from one decade to the next. But occasionally, and for no apparent reason, a glacier abruptly goes wild. It does not scurry at breakneck velocity but, creeping like a shadow, surges ahead at ten to one hundred times the average rate. Such glacial surges, once considered a rarity, can occur on any glacier. Glaciologists call them galloping glaciers.

The precise cause or causes of these glacial advances are not fully understood. Documentation of normal glacial movements shows that all the ice does not move at an equal rate. Friction with the bedrock floor slows the ice movement at the bottom of the glacier, and drag along the valley wall slows the movement along the sides. One theory suggests that if there were sudden melting of a glacier along the underlying bedrock the ice would be released to move rapidly down the slope. Another hypothesis proposes that a block of unmoving ice at the terminus of the glacier may function as a dam. Eventually, pressure from the flow of ice behind it forces the stagnant ice to give way and propels the glacial ice forward.

The physics of glacial movement is quite well established. By knowing the thickness, width, surface slope, and internal temperature, glaciologists can determine rather accurately the rate of growth and movement of any particular glacier. However, the galloping glacier does not follow the rules; unpredictably it may start to move at many times its normal rate and continue for days, weeks, or months. When a tranquil, smooth glacier begins to surge, it takes on an entirely new appearance, complete with sound effects. Ice streams break up in turmoil, a wave of ice bulges to the front, and the surface of the glacier buckles chaotically. The ice may shatter into sharp pinnacles the size of cathedrals. Cliffs of ice may split and crumble, accompanied by a deafening noise, or the glacier may flow along speedily but quietly for days.

Several galloping glaciers that have been studied show a somewhat regular period of surging. The Variegated Glacier, a 24—kilometer—long (15—mile—long) glacier northeast of Juneau, Alaska, has surged about once every 17 to 20 years since 1906.

The Vernagt Glacier in the Austrian Alps has surged four times since 1599, at seventy—four to ninety—three—year intervals. A surge that was expected in 1927 failed to materialize, and the Vernagt has not galloped since.

The largest glacier in the former USSR, the Fedchenko, normally moves about fifty yards per year, averaging five inches per day. Even that advance is relatively rapid for a glacier. Just a few years ago it unexpectedly surged and galloped at over fifty yards per day! This incredible pace continued for several weeks. Inhabitants of several villages had to flee from its path as the ice mass surged over their homes.

The natives of the Kutiah Valley in the Karakoram Range, west of the Himalayas, were less fortunate. On March 21, 1953, they saw glaciers of three valleys grow rapidly and pour great volumes of ice into the main valley. The large glacier advanced rapidly while the peasants watched forest, fields, and villages disappear under the ice. There was nothing they could do to halt the glacier, which moved at a rate of a hundred meters (328 feet) each day, or about sixteen feet an hour. On June 11 the advance came to a halt, but a new glacier seven miles long filled the valley and dammed the upper section, eventually creating a lake where the forests had been.

The Black Rapids glacier in central Alaska, which galloped in 1936, has been a source of well—witnessed stories of galloping glaciers. Near the highway was a hunting—fishing lodge that housed the caretaker and his family during the quiet season. Through the fall they constantly heard rumbling and felt the ground shake. They concluded, rather naturally, that it was an earthquake swarm. But they were wrong!

One December morning the caretaker's wife focused binoculars on a valley opening and shrieked an alarm. There she saw a gigantic wall of ice, a mile wide and over 300 feet high, bearing down on the lodge. As the ice moved forward, it cracked, throwing house—sized chunks of ice before it. They crashed to the ground in an icy spray, creating a terrible roar each time the ground was struck. The glacier moved at the rate of over 200 feet per day, and the lodge appeared doomed. But less than one—half mile from the lodge the movement stopped, and it has never surged again.

At present the glacier is in a stage of retreating through melting, but enough remains as a grim reminder of the time a mountain of ice almost galloped over the lodge. This has remained a prominent tale of suspense in local history discussions and never seems to lack an interested audience. Many listen with confirmed skepticism — they would have to see it to believe it.

From the book: 
Our Fascinating Earth