GEOLOGY 301 EXAM 2 QUESTIONS WITH DETAILED CORRECT ANSWERS

EARTHQUAKE - correct answers The shaking that results from the movement of rock beneath Earth's surface. P WAVES - correct answers A type of seismic wave that compresses and expands the ground. Travels through solid, liquid, or gas love waves - correct answers moves back and forth in a zigzag pattern Rayleigh waves - correct answers p waves that intersect the surface and moves like ripples in a pond. How to determine epicenter using seismographs? - correct answers first arrival of body waves depends on distance, so you can determine how far the station is from the epicenter radius. Depth of focus - correct answers shallow: divergent and transform intermediate and deep: convergent what generates faults and force? - correct answers normal hanging wall moves down relative to the footwall results from extension (stretching) reverse hanging wall moves relative to footwall results from compression slope of fault is steep slip-stick blocks inside lately past one another fault surface is nearly vertical no vertical block motion What happens at convergent boundaries during earthquakes? - correct answers subduction zone = frequent earthquakes What is the Mercalli scale? - correct answers intensity -shaking damage -Roman numerals assigned to different levels of damage zones -is damage diminishes in intensity with distance What is the Richter scale? - correct answers Logarithmic (1 unit increase=10 fold increase in magnitude) magnitude: amount of energy released - maximum seismograph motion -normalized for distance from epicenter - magnitude 6=hiroshima bomb What is the seismograph? - correct answers instrument that measure seismicity - reveals size and location of earthquakes - first wave causes frame to sink - next vibration causes the opposite motion What are tsunamis? - correct answers earthquake changes the sea floor - normal faulting= drops sea bed; trusting raises sea bed - Displaces volume of overlying water that race rapidly away - Frequent - Influence entire water volume waves come ashore as a raised plateau that pour onto land What is the viscosity of lava controlled by? - correct answers the silica content. mafic- less viscous felsic- more viscous - temperature of the lava - gas dissolve in the lava What is pyroclastic material and pyroclastic flow? - correct answers Pyroclastic material: dust, ash, cinder, block, bombs Pyroclastic flow: turbulent mixture of pyroclastic material and gases flowing down the slope of valance. what is an explosive eruption? - correct answers an eruption driven by the expansion of gases in a viscous magma and dominated by the generation of solid volcanic fragments. what are effusive eruptions? - correct answers Eruption dominated by lava flows - hot lava -less silica, more mafic, low viscosity - no trapping or gases What are shield volcanoes? - correct answers - broad, gently sloping - composed of basalt, layers of solidified lava flows - low viscosity lava What are composite volcanoes? - correct answers - composed of mostly andesite, alternating layers of pyroclastic fragments and lava flows. - built over long spans of time - intermittent eruptions that may be effusive or explosive - relatively resistant to erosion - more viscous, high in silica - occur near subduction zones what are cinder cones? - correct answers - composed of pyroclastic fragments ejected from a central vent, usually basalt. - smallest type of volcano - formed as the result of a buildup gases, independent of composition - exclusively constructed of pyroclasts What are calderas? - correct answers - volcanic depression much larger than the original crater - created when a volcanoes summit is blown off by exploding gases or when a volcano collapses into a partially emptied magma chamber - extremely violent eruptions what are lava domes? - correct answers - steep sided, dome shaped masses of volcanic rock formed from viscous lava that solidifies in or immediately above a volcanic vent -constructed of lava that is felsic or intermediate. - often form within the craters How does the type of bedrock or sediment composing a region influence the intensity of shaking during an earthquake? - correct answers Different materials will react differently to the same amount of stress. List and describe examples of volcanic hazards in general, and those that were important during the May 18, 1980 eruption of Mount Saint Helens in particular. What was the sequence of events that led up to the lateral blast? - correct answers volcanic hazards: pyroclastic flow, volcanic gases, lava flows, tsunamis, debris-flow Earthquakelandslideuncorked the chamberdebris flow avalanche How do the sizes of the "super" volcanic eruptions that occurred at Long Valley caldera and Yellowstone compare with the size of the eruption of Mount Saint Helens in May, 1980? What field evidence has allowed geologists to estimate the magnitudes of the Long Valley and Yellowstone events? - correct answers Long Valley and Yellowstone both had ash through several states, while Mt St Helens only had significant ash in Washington. The Volcanic Explosivity Index (VEI) was also evidence used. Mt St Helens was a 3.5 VEI, while Long Valley and Yellowstone were between 7 and 8 VEI.