TO:Lisa A. Sarvestaney, M.A., Instructor

MEMO

TO:Lisa A. Sarvestaney, M.A., Instructor

FROM:Charles Lewis

DATE:29 November, 1998

RE:Earth Science Exam

1.“Erosion caused by gravity acting directly is called mass movement” (508). PE becomes KE and occurs when cohesive forces are reduced and/ or friction is reduced. It is classified by three categories: material--bedrock or debris (soil, rock, fragments, snow); rate--fast to minuscule; and type--fall, slip, flow, creep. Examples are rock fall, rock slide, and mud flow.

2.Characteristics of deposited materials by category: wind--dune (mound of sand) and loess (fine dust or silt that originated as rock flour); streams--dissolved rock materials carried in solution, clay minerals and small grains carried in suspension, and sand and larger fragments that are moved along the stream bottom; and glaciers--moraines (bulldozed rock), skree (rocks smaller than your fist), and rock flour (powder).

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4.An igneous mineral (inorganic matter with a crystaline structure) bursts forth from a vent of a volcano and eventually settles to earth as ash. This ash is washed down stream and settles into a lake bottom. Over the course of many years, the mineral is exposed to compaction and cementation. A new sedimentary rock is now formed from the original material.

5.As a river ages, it changes the landscape by eroding its channel. In its youth, it predominantly erodes downward creating a V-shaped channel. In maturity, the stream eventually erodes boulders, rapids, and waterfalls smoothing and lowering the stream gradient creating a wider flood plain that occupies the valley floor. As the stream ages into old age, the valley becomes broad; the gradient is much lower; and the stream flows slowly in broad meanders eventually creating ox-bow lakes. Incidently, a stream or river may exhibit all of these characteristics at the same time. The age of the stream is determined by the average characteristics over the entire length.

6.The asthenosphere is “a hot, elastic semi-liquid layer that extends unbroken around the entire earth” (464). It is located approximately 130 to 160 km below the earth’s surface and is part of the earth’s mantle. Plate tectonics are believed to be a result of “slowly turning convective cells in the plastic asthenosphere . . .” (473).

7.Folding is the result of the bending of layers of rock--plastic strain--and happens deep within the surface of the earth. Folding is characterized by high pressure, high temperature, and a slow process. Pressure is applied in opposite and parallel directions. Faulting however happens to the more brittle rock near the earths surface. It is characterized by low pressure, low temperature, and a relatively quick process. Pressure is applied in opposite but non-parallel directions. At some point, the stress exceeds the cohesive forces and a break occurs.

8.“A stress is a force that tends to compress, pull apart, or deform a rock” (482). Compressive stress is two plates moving together. Tensional stress occurs when one plate moves away from another. Shear stress is produced when two plates slide past one another. “The adjustment to stress is called strain” (482). In elastic strain, the rock unit recovers its original shape. In plastic strain, the rock units are molded or bent and do not retain their original shape. And in fracture strain, rock units crack or break.

9.How do rocks differ from minerals? “A rock is a solid aggregation of one or more minerals that have been cohesively brought together by a rock forming process” and “a mineral is defined as a naturally occurring, inorganic solid element or compound with crystalline structure” (442). In plain English, a rock is a jumble of elements and minerals formed under high temperature, pressure, and time. A mineral can be a rock; however, a rock is not a mineral. The key qualifier is the crystalline structure. Ice is not a rock, but it qualifies as a mineral under this definition.

10.A P-wave is a longitudinal wave that travels quickly through gas, liquid, and solid at approximately 7 km/s. As some of the waves are reflected to the surface of the earth, seismologists can measure them. By multiplying the speed of the wave by the time it took to reach the seismograph, you can determine the distance to the epicenter. Take a map and draw a circle with a radius equivalent to the distance to the epicenter. If three seismologists record the incoming shock wave and draw their circles, you can determine the location of the epicenter (triangulation).

An S-wave is a transverse wave that only moves through a solid at approximately 2 km/s. S-waves are reflected at different angles from P-waves. Different locations measure the waves. By triangulating these readings and comparing them to the readings from the P-waves, seismologists can determine the focus of the earthquake.

11.A. “Convection is the transfer of heat by a large-scale displacement of groups of molecules with relatively higher kinetic energy” (92).

B. Convection is believed to be the cause of plate tectonics. As magma heats and cools in the plastic asthenosphere, the circular movement causes the tectonic plates that float on the asthenosphere to move in predictable directions.

C. Convection causes the moderate summer weather in Anchorage Alaska. As warm, moist air passes over Portage Glacier from the Pacific Ocean to Cook Inlet, it is cooled and the relative humidity increases. As a result, the cooler air descends to surface level and precipitates. The result is an average temperature of only about 60o F and a high rainfall in the summer.