Measurement of the thickness

The thickness of a glacier can be obtained, with special formulae, once the speed, inclination and width are known along with some characteristics of the ice such as its density and viscosity. However, since these parameters are difficult to evaluate and vary in different parts of the glacier, it is a very rough estimate.
The oldest and most direct method of measuring the thickness of a glacier consists in digging a hole that reaches the rock substratum. However, this method is very expensive, it requires heavy machinery difficult to transport, especially in the mountains and gives the thickness only at a fixed point and not along the entire glacier. The ice is extracted by perforation in the form of long and thin cylinders called “cores” and can be studied to obtain a lot of information.
An indirect method of measuring the thickness of a glacier is by using geophysics, a special branch of geology that studies anomalies in the Earth’s gravitational field and the propagation of seismic and electromagnetic waves in order to obtain information about the substances that compose the Earth’s crust, including the ice of the glaciers. Seismic reflection profiling is the most commonly used technique for glaciers: blasting an explosive charge or ramming a heavy hammer on the surface of the ice generate waves that travel in the ice and are reflected by the underlying bedrock. By studying the course of the waves and knowing the speed at which they travel in different materials it is possible to calculate the thickness of the ice. Electric profiling , instead, is based on the study of the difference in potential created by the passage of electric current between two measuring points inserted in the ice, utilising the different conduction properties of ice and rock. A recent technique, that is very fast and efficient, is based on the reaction of ice to radar waves passing through it as if it were transparent. The novelty of this technique is that the required instruments can be placed on airplanes that can fly over vast areas: in this way, in fact, it has been possible to reconstruct the morphology of the bedrock and ice-sheet thickness in Antarctica and Greenland. This innovative technique was discovered by chance by some pilots who noticed the ‘anomalous’ behaviour of the radar altimeters on board their planes while they were flying over the Antarctic.

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