Lecture 4 Natural Hazards Flashcards
(40 cards)
What is mass movement in geology?
The downslope movement of rock, regolith, and soil under the direct influence of gravity.
What step does mass movement follow in the evolution of most landscapes?
Weathering. Landscape changes due to weathering - weathered and broken apart rock debris transfers downslope, carried by a stream/glacier.
What determines whether a slope fails or not?
- Relative force (gravity) size. 2. Resistance strength of the rock/soil.
What is a trigger in mass movement?
The last of many causes that forces the condition of a slope from stable to unstable and causes mass movement.
What are the common triggers of mass movement?
- Saturation of material with water. 2. Oversteepening of slopes. 3. Removal of anchoring vegetation. 4. Ground vibrations from earthquakes.
What is the role of water in mass movements?
Water (as rain/snow) saturates surface materials, allowing gravity to more easily set the material in motion as cohesion among particles is decreased.
Give an example of a mudslide case.
January 2005, La Conchita, California. 10 people dead.
What is the role of oversteepened slopes in mass movements?
Materials from the base of the wall are removed, increasing downslope forces and reducing resisting forces, producing unstable slopes.
What is the angle of repose and what does it depend on?
The steepest angle at which loose materials remain stable. Depends on the size and shape of particles, typically 25 to 40 degrees.
What is the role of vegetation in preventing mass movements?
Prevents erosion and the root system binds together soil and regolith to promote slope stability.
Example illustrating the anchoring effect of plants.
Menton, France. Deep-rooted olive trees replaced by shallow-rooted carnabons led to landslide issues.
How do earthquakes act as a trigger?
Conditions that favor mass movement may exist in an area; earthquakes and aftershocks can trigger this.
What is liquefaction?
The phenomenon of transforming somewhat stable soil into mobile material capable of rising toward Earth’s surface.
What is used to classify mass movements?
- Types of material. 2. Types of motion. 3. Rate of movement.
Discuss fall as a type of motion.
Involves the free fall of detached individual pieces of any size, characterized by steep slopes.
Describe slide as a type of motion and its types.
Distinct zone of weakness separating the slide material from the more stable underlying material. Types include: 1. Rotational slides - surface of rupture is concave-upward. 2. Translational slides - material movement along a relatively flat surface.
What is flow as a type of motion?
Material moves downslope as a viscous, often turbulent fluid, mostly saturated with water and moves as lobes or tongues.
What is a rock avalanche?
A type of mass movement termed a rock avalanche.
Example: Peruvian Volcano - Nevados Huascaran.
What is a slump?
A mass of rock or unconsolidated material moving as a unit along a curved surface. Not fast or far-reaching. Common in clay.
Example of a rotational slide.
What are rockslides and debris avalanches?
Blocks of bedrock break loose and slide down a slope. Blocks of unconsolidated material are called debris slides.
How do rockslides lead to avalanches?
After initial sliding, material can break down into chaotic debris avalanches.
Where do rockslides usually take place?
They take place in inclined rock strata, usually where joints and fractures exist parallel to the slope.
What is debris flow?
A relatively rapid type of mass movement involving a flow of soil and regolith containing a large amount of water.
When is a debris flow called a mud flow?
When material is primarily fine-grained.
