Consider the following features about a geographical phenomenon :

1. Torrents of snow and ice roaring down a steep mountainside

2. It is hazardous to skiers and mountaineers

3. It involves a mix of falling, rolling, sliding and flowing of materials

Which of the following phenomena can be identified with the above features?

The correct answer is Avalanche.

Key Points

• Avalanche
  • It is a mass of material moving rapidly down a slope.
  • An avalanche is typically triggered when the material on a slope breaks loose from its surroundings; this material then quickly collects and carries additional material down the slope.
  • When a mass of snow moves rapidly down a slope of a mountain is known as Avalanche. 
  • There are various kinds of avalanches, including rock avalanches (which consist of large segments of shattered rock), ice avalanches (which typically occur in the vicinity of a glacier), and debris avalanches (which contain a variety of unconsolidated materials, such as loose stones and soil).
  •  It involves a mix of falling, rolling, sliding and flowing of materials.
  • The size of an avalanche can range from a small shifting of loose snow to the displacement of enormous slabs of snow.
  • In a slab avalanche, the mass of descending snow may reach a speed of 130 km (80 miles) per hour and is capable of destroying forests and small villages in its path.
  • It is hazardous to skiers and mountaineers.
  • Avalanches also have been triggered intentionally in warfare to kill enemy troops.
  • Avalanches contain three main features: the starting zone, the avalanche track, and the runout zone. Avalanches launch from the starting zone. That’s often the most unstable part of the stope and generally higher on the mountain.
  • Once the avalanche starts to slide, it continues down the avalanche track, the natural path it follows downhill. After avalanches, large clearings or missing chutes of trees provide clues to an avalanche’s trajectory.
  • The avalanche finally comes to a stop at the bottom of a slope, in the runout zone, where the snow and debris pile up.
• Hence, Option 2 is correct.

Additional Information

• Slump and earthflow
  • Earth flows are made up of disintegrating soil and weathered rock, which moves by inter-particle or inter-layer shear above a failure plane in the underlying rock.
  • The failure plane may be either planar or curved.
• Landslide
  • It is defined as the movement of a mass of rock, debris, or earth down a slope.
  • Landslides are a type of "mass wasting," which denotes any down-slope movement of soil and rock under the direct influence of gravity.
• Rockslide
  • It is a type of landslide caused by rock failure in which part of the bedding plane of failure passes through compacted rock and material collapses en masse and not in individual blocks.
  • Note that a rockslide is similar to an avalanche because they are both slides of debris that can bury a piece of land.