Modeling Ice Friction

Glaciers and Ice Friction

Glaciers are comprised of snow accumulated over many years and compressed into large ice masses. Formed when snow remains in a location long enough to form ice, glaciers are unique in that they have the ability to move, flowing like extremely slow rivers due to their sheer mass.

Glaciers currently occupy approximately 10 percent of the world’s land surface, mainly in the polar regions and contain approximately 75 percent of Earth’s fresh water. Both percentages clearly indicate the importance of the relationship between human life and the health of the glaciers.

Glaciers move because of their immense weight, or the force of gravity. Movement occurs in different directions: down mountain valleys, across plains, or even out into the sea. The bottom of a glacier moves slower than the upper levels due to the friction created between the ice and the ground beneath it.

The roughness of the ground’s surface beneath the glacier, the temperature of the surfaces in contact with each other and the incidence of cavities filled with water all influence the level of friction and consequently the speed at which the glacier flows. As these changes occur under the massive size of the glacier, it is difficult to measure the exact parameters.

Measuring these parameters continues to gain in importance due to the relationship between the melting of glaciers and global warming. Global warming and the resulting glacier melt leads to a variety of issues including, but not limited to, a shortage of freshwater, excessive flooding, animal extinction, disappearance of coral reefs, reappearance of lethal diseases and disruption of weather patterns.

In the article “A New Model of Ice Friction Helps Scientists Understand How Glaciers Flow” published on December 18, 2018 by the American Institute of Physics, Professor Bo Persson of the Jűlich Research Center in Germany, well-known in the field of tribology, describes a new model for examining ice friction.

Professor Persson is famous for his studies of rubber friction and adhesion and in the current research he used the knowledge gained from past studies to develop his model of ice friction. Taking this tribology knowledge and experience and applying it to glaciers, Persson specifically examined how different factors affected ice friction and glaciers. These factors included the roughness (unevenness) of the contacting surfaces of ice and bedrock as well as the effect of regelation, which is the concept of ice melting while under pressure and then refreezing as the pressure is reduced. Regelation only occurs with substances that expand when frozen. Pressure beneath glaciers is not constant due the roughness of the ground surface. Higher pieces of ground increase the ice pressure as the glacier moves over that bump, thereby increasing the temperature and reducing the level of friction. Moving on from that higher piece of ground the pressure reduces, decreasing the temperature and then the level of friction increases. The cycle continually reoccurs at different rates and locations, depending on the roughness of the ground surface.

Bo Persson’s study examines how cavities under the glacier form throughout the moving process. These cavities are typically filled with pressurized water as the temperature between the two surfaces of ice and ground is close to the melting temperature. These water-filled cavities reduce friction by reducing the weight load of the glacier and providing lubrication, ultimately resulting in glaciers gaining speed.

Unfortunately, current models are unable to accurately depict this situation regarding how the roughness of the ground surface affects the flow of glaciers. With the ever-increasing changes in our world’s climate, this becomes of key importance to future studies, studies that will hopefully provide the needed knowledge to reduce glacier loss and save our planet from future catastrophic destruction.

Further information in the original article: B. N. J. Persson, “Ice friction: Glacier sliding on hard randomly rough bed surface,” Journal of Chemical Physics (2018). DOI: 10.1063/1.5055934