Week nine Flashcards

Question

How to classify mass movements?

Answer 1

Flow occurs on different scales. Creep is slow and only detected by dislocation or bending of features at the surface, whereas debris avalanches are very rapid flows of rock, regolith, vegetation, and/or sometimes ice. Ø Rock falls are common where the rock is highly jointed and on a steep slope, such as New Hampshire’s “Old Man of the Mountain,” which collapsed in May 2003.

Answer 2

The loose material that piles up at the base of steep slopes is called talus. The lack of vegetation or soil on talus indicates that material is actively Accumulating

Answer 3

- move downslope in contact with a surface of rupture, typically along bedding planes, foliation, or joint planes oriented parallel to the slope. – If the rupture surface curves, then the slide mass rotates as it moves downslope, causing rock layers and surface features to tilt. The curved rotational slide surfaces are scoop shaped, and they usually form in regolith or poorly consolidated or weak rock where bedding or joints do not influence failure. This is called a slump.

Answer 4

Flows are the continuous movement of rock, regolith, or both that behave like a high-viscosity liquid. Figure 6.7a illustrates the “liquid” appearance of moving flows.

Answer 5

Are detected only by dislocation or bending of features at the surface like these sedimentary layers and trees.

Answer 6

Under the conditions below, a brick on a board will slide if tilted far enough. What does this mean? 1) Increasing slope favors motion or slope instability. Next, we may sand the board and find it moves more easily. 2) Smoother surfaces favor motion and slope instability, and if we wet the board, it moves easier still. 3) The presence of water favors motion and slope instability. This simple set of experiments suggests that slope, surface roughness, and water are factors affecting the balance between driving and resisting forces.

Answer 7

For motion to happen, the gravity force parallel to the surface (called the driving force) must be greater than the resisting strength.

Answer 8

Friction is the force that opposes motion between two objects that are touching one another. The friction increases as the roughness of the surfaces increases. Friction also varies with slope angle because on lower slopes the weight of fragments pulls them down in stronger contact with underlying material.

Answer 9

the other component of resisting strength, is the attraction of particles at the atomic level. Materials such as loose sand and gravel have very little cohesion between particles, but clay particles, with charged surfaces, have high cohesion.

Answer 10

Angle of repose: the maximum angle of a stable slope as determined by the friction, cohesion, and particle shape eg: adding small amounts of water to sand initially increases cohesion between particles, but too much water leads to failure

Answer 11

Vegetation is a very important factor in slope stability. Roots penetrate and bind together regolith and absorb water from precipitation.

Answer 12

These figures illustrate the role of vegetation plus climate in determining the thickness of regolith on hillslopes. Here in a temperate mid-latitude forest, we have dense tree cover and thick regolith. As a result, slopes tend to be fairly stable. Mass movement occurs, but generally it is slow-velocity types such as creep, slumps, and flows.

Answer 13

In arid regions with low vegetation abundance and slow rates of weathering, surface-water removes most regolith particles almost as quickly as they loosen from bedroom. Mass movements are typically rock falls and slides

Week nine Flashcards

(37 cards)