MASS WASTING Flashcards
as a geomorphic process where soil, sand, regolith, and rock move downhill, often as a solid or discontinuous mass. Gravity plays a significant role in this movement, and the process may exhibit flow-like characteristics.
MASS WASTING
___________,__________ can be triggered by factors like heavy rain or snowmelt saturating surface materials. This water doesn’t transport the material but makes it easier for gravity to set it in motion. When sediment pores are filled with water, cohesion among particles is disrupted, reducing internal resistance and allowing materials to move more easily. Water also adds weight to the material, which, combined with reduced internal resistance, can lead to downhill movement, such as sliding or flowing.
- THE ROLE OF WATER, MASS WASTING
can trigger mass movements. This occurs when slopes become excessively steep, often due to natural processes like a stream cutting into a valley wall and removing material from its base. Human activities can also contribute to oversteepening, creating unstable slopes that are prone to mass wasting.
- Oversteepened Slopes
plants play a protective role against erosion and contribute to slope stability by binding soil and regolith with their root systems. They also shield the soil surface from erosional effects caused by raindrop impact. In the absence of vegetation, particularly on steep slopes with ample water, mass wasting is more likely to occur. The removal of anchoring vegetation, whether through forest fires or human activities such as timber harvesting, farming, or development, often results in the downslope movement of surface materials.
- REMOVAL OF VEGETATION
areas conducive to mass wasting may remain stable for a long time until an additional factor triggers movement. One significant and dramatic trigger is earthquakes, which can dislodge large volumes of rock and unconsolidated material. Intense ground shaking during ___________ can lead water-saturated surface materials to lose strength, transforming into fluid-like masses that flow, a phenomenon known as liquefaction.
- EARTHQUAKES
rapid mass-wasting events do not always require a specific trigger such as heavy rains or an earthquake. Some events occur spontaneously. An example is the landslide at Sacred Falls State Park in Hawaii on May 9, 1999, where a mass of rock descended a nearly vertical slope without a discernible external trigger, resulting in fatalities and injuries.
- Landslides Without Triggers?
the classification of mass-wasting processes is based on the material involved in the movement. If the descending mass originates from unconsolidated material like soil and regolith, terms such as debris, mud, or earth are used. Conversely, if the mass involves bedrock breaking loose and moving downslope, the term rock may be included in the description.
- Type of Material
In addition to characterizing the type of material involved in a mass-
wasting event, the way in which the material moves may also be
important. Generally, the kind of motion is described as either a fall,
a slide, or a flow.
a. _______
b. ______
c. _______
- Type of Motion
when individual pieces of any size freely fall in a mass-wasting event, it is called a fall. This type of movement is common on extremely steep slopes where loose material cannot stay on the surface. The fallen rock may either drop directly to the base of the slope or move in a series of leaps and bounds over other rocks, and rock falls are a significant process in the formation and upkeep of talus slopes.
A. FALL
many mass-wasting processes are categorized as slides, indicating movements where a distinct zone of weakness separates the sliding material from the more stable underlying material. Two main types of slides are recognized. Rotational slides have a surface of rupture shaped like a concave upward curve, resembling a spoon, with the descending material showing a downward and outward rotation. On the other hand, translational slides involve material moving along a relatively flat surface, such as a joint, fault, or bedding plane, with little rotation or backward tilting.
B. Slide
The third type of movement common to mass-wasting
processes is termed flow. Flow occurs when material
moves downslope as a viscous fluid. Most flows are
saturated with water and typically move as lobes or
tongues.
C. Flow
some mass-wasting events involve exceptionally rapid rates of movement. For instance, the debris on Peru’s Nevados Huascaran slopes is estimated to have moved at speeds exceeding 200 kilometers (125 miles) per hour. The fastest type of mass movement is termed a rock avalanche. Researchers have found that rock avalanches, like the one depicted in Figure 10.6, essentially “float on air” as they move downslope. This occurs when air becomes trapped and compressed beneath the falling debris, enabling it to move as a buoyant and flexible sheet across the surface.
- Rate of Movement
_________ is a slow and long term mass movement. The combination of small
movements of soil or rock in different directions over time are directed by gravity gradually
downslope. The steeper the slope, the faster the creep. The creep makes trees and shrubs
curve to maintain their perpendicularity, and they can trigger landslides if they lose their root
footing.
Creeps
A _________, also called a ________, is a slow or rapid movement of a large mass of
earth and rocks down a hill or a mountainside. Little or no flowage of the materials occurs on
a given slope until heavy rain and resultant lubrication by the same rainwater facilitate the
movement of the materials, causing a landslide to occur.
LANDSLIDES
___________ is the process of introducing trees and tree
seedlings to an area that has previously not been forested.
Afforestation can be done through tree planting and seeding,
naturally or artificially.
AFFORESTATION
