| [Visitor (112.0.*.*)]answers [Chinese ] | Time :2022-04-28 |  There are often many fissures in the surface of glaciers, some of which are tens of meters deep. The presence of fissures indicates that glaciers are brittle. However, after hundreds of years of investigation and observation, the fissures on the glacier rarely exceed sixty meters deep. Most fissures close much smaller than this depth. This in turn shows that the lower part of the glacier is plastic, and it can be "soft" to adapt to various external forces without rupture. Therefore, the glacier can be divided into two layers, the layer that is easy to break on the surface is called the brittle zone, and the lower "soft" layer is called the plastic zone. The presence of plastic zones is the root cause of glacier flow.
In the case of force, in order to adapt to or eliminate external forces, the object can be deformed in three ways, namely elastic deformation, plastic deformation and brittle deformation (or rupture). Generally, objects have these three deformation stages when they are subjected to force. For example, a spring, in general, is elastically deformed; When the force exceeds the elastic strength, it is plastically deformed, and the spring cannot return to its original position; When the force exceeds the cracking strength, the spring is pulled off and deformed in brittleness. However, whether these three stages have a master or a subordinate, the three stages are not equally divided. What kind of deformation is the main one depends on the nature of the material itself.
As far as ice is concerned, because it is easy to achieve internal sliding of the crystal, it is conducive to exhibiting plastic deformation. However, when the external force suddenly increases, it is easy to exceed the cracking strength of the ice, and brittle deformation (fracture) occurs. We know that when an object is subjected to a long-term force, even if the force is small, it will produce plastic deformation. In the lower part of the glacier, due to the pressure of the upper ice layer and the thrust of the upstream ice layer, it is always in a state of stress, so that the plasticity of the lower ice layer is more fully expressed. At the same time, the melting point of the lower ice layer is slightly lower than that of the upper ice layer, so that the lower ice layer is closer to the melting point, so plastic deformation is easier to achieve.In this way, it is not difficult to understand the emergence of plastic belts in the lower part of the glacier. The surface layer of the glacier lacks the important condition of long-term stress, and when the external force suddenly increases, it is often deformed by elasticity or brittleness, becoming a brittle band...
In a smooth valley, the maximum flow rate of the glacier occurs on the surface of the glacier when it flows, and the speed decreases as it gets closer to the bottom of the valley, which is called gravitational flow. If, during glacier motion, it encounters a blockage of protruding bedrock or slower ice in front of it, there is a shear stress of pre-squeeze and post-compression, which is called blocking gravity flow. Where blocking gravity flow occurs, there are often many reverse faults in the ice, and complex folds appear. |
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