Firn
and Ice Formation
In the accumulation zone, snow falls and does not melt.
According to Roger LeB. Hooke, "The first phase of the
transformation of snow into ice involves diffusion of water
molecules from the points of snowflakes to their centers." This
is demonstrated in part a of the diagram below.
(Hooke)
This process occurs because vapor pressure is inversely
proportional to the radius of curvature, also known as the
Kelvin effect. This reduction of surface area means the snow
particles are packed together more densely with less oxygen in
between molecules. When a snowflake becomes rounded off and
spherical in shape, it is called firn. The firn on a glacier is
responsible for the formation of new ice. (Hooke)
Why Glaciers Flow
As the ice becomes thicker, so does the pressure on the bottom of the ice, and this is what causes movement. Increased pressure decreases the melting point of any substance, so the pressure of glaciers makes the ice deform underneath and slide slowly and fluidly. (Knight) According to Dr. Fountain, “Deep in the glacier, where the ice experiences the weight of all the snow, firn, and ice above, the ice is softer and deforms much like "silly putty" such that the stiff surface layers ride on the deforming softer layers deeper in the ice.” It is also important to note that because the movement of the glaciers is attributed to pressure, winter temperatures do not stop a glacier from moving. In a discussion about the study of glacier surfaces, researcher Matt Hoffman described the melt water of a glacier as lubricating the surface underneath the ice, which reduces the friction force between the glacier and the rocks underneath, which causes it to move at an increased velocity. (Hoffman)
(Fountain)
"Cross section of a typical alpine glacier...The blue arrows show the direction and speed...The longer the arrow the faster that ice is moving." (Fountain)
Regelation
Another process relevant to the physics of glaciers is called
regelation. One of the simplest methods of demonstrating this is
by weighting a wire over a piece of ice. Chang Q Sun with the
Nanyang Technological University in Singapore conducted this
experiment and explains, "The pressure the wire exerts on the
ice will melt the local ice gradually until the wire passes
through the entire block of ice. The water refreezes behind the
path of the wire so one can pull the wire through the ice, while
leaving the ice cube intact." He goes on to explain that the
mass of a glacier has enough pressure force on the lower surface
that the melting point decreases, and the ice will melt, which
allows the glacier to slide. (Sun)