Week 4 Flashcards
Denudation
: In geology,involves the processes that cause the wearing away of the Earth’s surface by moving water, by ice, by wind and by waves, leading to a reduction in elevation and in relief of landforms and of landscapes.
Shear Stress
: stress resulting from application of force parallel to a surface (force pulling the boulder/grain downslope)
Normal Stress
: component of stress perpendicular to the Earth’s planar surface (force keeping the boulder/grain from moving)
For rounded boulders, the critical angle of repose is
about 35°
Rounded dry sand grains on a pile will stand no steeper than
approx. 30°
Porosity
or void fraction is a measure of the void spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%; the quality or state of beingporous; the ratio of the volume of interstices of a material to the volume of its mass
Factors that influence downslope movement
- slope angle
- critical angle of repose
- material strength
- cohesion & water saturation
Material Strength
Solid rock are strong and unlikely to slide; the exceptions are rocks that contain weak zones such as sedimentary layering or strongly developed zones of fracturing; they are especially likely to fail if their zones of weakness are aligned parallel to a slope, or if a steep slope is created during construction
Laminar
– the lower part of the soil often moves under the pressure of the heavy materials above; the movement will trigger downward movement of the upper soil
Solifluction
- flowage of water-saturated soil down a steep slope. Becausepermafrostis impermeable to water, soil overlying it may become oversaturated and slide downslope under the pull ofgravity. Soil that has been opened and weakened by frost action is most susceptible. Movement is at a maximum rate of a few inches per day, eventually producing smooth, gentle, concave slopes. Original stratifications of the soil become contorted if not completely destroyed.
Gelifluction(congelifluction)
The slow flow of water-lubricated, unsorted material and rock debris over perennially frozen ground, and on slopes as low as 1°. It is the cold-climate variety ofsolifluction and occurs only in theactive layer(usually to a depth of 3 m); interglacial landscapes; freeze and thaw process;
Gabions
is a cage, cylinder, or box filled with rocks, concrete, or sometimes sand and soil for use in civil engineering, road building, military applications and landscaping. For erosion control, caged riprap is used.
Debris flows and mudflows
are among the most dangerous of downslope movements because of their sudden onsets and high velocities; predominantly involve silt and clay sediments. The flows that occur in Leda Clay deposits along the Sanguenay, St. Lawrence etc; thick accumulations of clay or silt such as regions that were flooded by glacial lakes during glacial retreat
Dendritic pattern
so called because of their similarity to branching organic forms, are most common where rocks or sediments are flat-lying and preferential zones of structural weakness are minimal.
Debris Flow
involve mostly sediment, such as glacial deposits and materials moved down from higher areas by rivers and gravity. All sizes of material, from clay to boulders and broken rock fragments can be involved in a debris flow; speeds range from metres per hour to tens of km per hour, depending upon the steepness of the slope and the amount of water involved. Although debris flows are more common in mountainous areas, any steep slope with unstable sediment can fail as a debris flow, as occurred at Daniel’s Harbour, NFL.
