What is debris avalanche or flow?

A debris avalanche is the sudden catastrophic collapse (landslide) from an unstable side of a volcano. Many volcanic cones are steep sided and unstable due to rapid growth of the cone. Debris avalanches can be wet, dry or both, and if wet, an avalanche may evolve and continue to flow further down slope as a lahar.

What is the main difference between a rock avalanche and a debris avalanche?

This scaling differs substantially between the two major types of long-runout landslides, partly owing to differing material properties: rock avalanches initiate on dry (unsaturated), massive, and variably jointed rock slopes, whereas volcanic debris avalanches are made up of a mixture of loose debris and solid rock …

What is the difference between debris flow and mud flow *?

A debris flow (commonly called a mud slide) is a moving mass of loose mud, sand, soil, rock, water and air that travels down a slope under the influence of gravity. A mud flow is the sandy, more water-saturated analog of a debris flow.

What causes a debris flow?

Debris flows can be triggered in a number of ways. Typically, they result from sudden rainfall, where water begins to wash material from a slope, or when water removed material from a freshly burned stretch of land. Another major cause of debris flows is the erosion of steams and riverbanks.

What’s the average speed of a debris avalanche?

A debris avalanche (Figure 1) is a fast-moving debris flow that travels faster than about 10 mph or approximately 25 yards in about 5 seconds. Speeds in excess of 20 mph are not uncommon, and speeds in excess of 100 mph, although rare, do occur locally. Figure 1. Sketch of a typical debris avalanche scar and track.

Which is worse an avalanche or a landslide?

These geological disasters occur on slanted regions and they can cause massive damages especially when they occur near residential areas. The impact of either an avalanche or a landslide is defined by the underlying geology, speed of flow, distance traveled, and generated debris.

Can a rain storm cause a debris avalanche?

Most rainstorms are of such low intensity that they do not trigger debris avalanches. Some intense storms may trigger only a few debris avalanches. However, when the ground is already saturated from previous rain, even relatively short high-intensity rainstorms may trigger debris avalanches.

How does an avalanche grow as it accelerates?

Avalanches tend to grow in volume and mass as they accelerate down the slope. When the snow is accelerating at a very high speed, some of the snowflakes can blend with air and create a gravity current known as powder snow avalanche.