The carbon cycle – carbon is stored in the atmosphere in the form of carbon dioxide, which is absorbed by plants and converted to carbohydrates by the process of photosynthesis. The cycle then follows food chains, with carbohydrates being consumed by herbivores and then carnivores, being metabolised during the process of respiration. Carbon dioxide is returned to the atmosphere as animals exhale and when organic waste and dead organisms decay. Vegetation and animals are thus important stores of carbon, although that carbon may be rapidly returned to the atmosphere if vegetation is burned. Atmospheric carbon dioxide is soluble in water, in which it forms carbonic acid, which forms bicarbonate ions and carbonate ions, which in turn form salts .
This subjects the slope to higher than normal shear stresses, leading to potential instability. A slide is a mass movement where the material moves as a coherent mass. A slump is a type of slide that takes place within thick unconsolidated deposits . Slumps involve movement along one or more curved failure surfaces, and are thus rotational slope failures. Slumps have downward motion near the top and outward motion toward the bottom (Figure 15.14).
The percent value is written on the gridded overlay next to the grid intersection. There are several considerations to keep in mind when gathering data on existing landslides. First, the time and effort required to conduct an inventory varies with geologic and topographic complexity; size of an area; and desired level of sona uf inventory detail . Figure characterizes the relationship between the amount of time and level of effort for these three variables. Second, more detailed inventories will require larger map scales to reveal the small features of this added detail. Third, additional data gathering can add detail to an existing inventory.
Dissolved load earth material in a stream that has been dissolved into ions and carried in solution. Differentiation the process by which a magma forms different minerals according to changes in temperature and pressure. Depth of focus of an earthquake, the distance between the epicenter and the focus. Cross-bedding a sedimentary structure in which the bedding planes of a particular unit are inclined compared to the bedding of the enclosing rocks. Continental slope an area that extends from the seaward edge of a continental shelf into the deep ocean at an average angle of 4 to 5 degrees. Continental glaciation glaciation that affects a broader, flatter part of a continental land mass than does alpine glaciation.
Mud flow the movement of a liquidy mass of soil, rock debris, and water down a well-defined channel. Liquefaction of a landslide, an occurrence in which water-saturated soil moves downslope like a liquid. Debris flow a mass-wasting event in which movement and turbulence occur throughout the mass. As a consequence, in the description of a landslide, it can be interesting to understand in what type of climate the event occurred. This criterion describes, in a general way, the location of landsides in the physiographic context of the area.
A transparent overlay with a 2cm x 2cm grid is placed over the landslide inventory map. (See Figure for a graphic depiction of each step.) At each grid intersection a transparent gridded circle 2.5cm in diameter is centered on each grid intersection on the transparent overlay. The number of grid squares in the circle through which landslide deposits are visible is counted. Divide this number by the total number of grid squares within the inscribed circle. This yields the proportion of the unit area within the circle that is underlain by landslide deposits. This proportion is multiplied by 100 and rounded off to the nearest whole number to compute the percentage of landslide-disturbed terrain.
Trees with curved trunks are often signs that the hillside is slowly creeping downhill. The white areas on green hillsides mark scars from numerous mudflows. Deposits became unstable and flowed down in a valley covering 40 homes and killing 43 people.
Foreshock one of the small earthquakes that may precede the main earthquake. Foreland basin a shallow continental basin behind a magmatic arc, a result of subsidence. Foliation the alignment of parallel layers or bands of mineral grains in a rock subjected to prolonged differential stress and/or shearing. Flash flood flood resulting from very heavy rainfall over short periods. Fault an area in which rock has been displaced along a fracture, such as having one side that is moved up or down.
Sufficient understanding of landslide processes does exist, however, to be able to make an estimation of landslide hazard potential. The planner can use this estimation to make certain decisions regarding site suitability, type of development, and appropriate mitigation measures. Assessing relative landslide hazard is the objective of the method described in this chapter. Its primary product, a landslide hazard map, provides planners with a practical and cost-effective way to zone areas susceptible to landsliding.
