Study Guide
Geology 303, SDSU Spring
PEOPLE for TEST 1:
1) Alfred Wegener: the most famous and outspoken proponent of continental
drift. German meteorologist. Put evidence together that supported the idea
that all the continents were unified into a single landmass and called it
Pangaea (all-earth).
2) Steno (Niels Steensen): Danish physician who developed several laws that are
fundamental in interpreting geologic history. These include the laws of original
continuity and superposition.
NATURAL DISASTER CASE HISTORIES for TEST 1:
1) Lisbon earthquakes (Chapter 3);
2) Lituya Bay, Alaska, 1958 (Chapter 8);
3) Tsunami of 2004, Indian Ocean (Chapter 8);
4) Krakatoa eruption of 1883 (Chapter 8);
5) Crescent City, California, tsunami during 1964 (from 1964 Good Friday
Earthquake in Alaska-Chapter 8);
6) The great 1700 earthquake along the Cascadia Subduction Zone (Pacific
Northwest-Chapter 4);
7) Mexico City earthquake of 1985 (Chapter 4);
GEOLOGY TERMS/CONCEPTS for TEST 1:
1.(2)-asthenosphere: The layer of the Earth below the lithosphere in which
isostatic adjustments take place; the asthenosphere is about 200 km thick. The
rocks here deform readily and flow slowly (see ductile or plastic behavior).
2.(2)-uniformitarianism/actualism: Uniformitarianism (“The present is the key to
the past”) is the concept that the same laws and processes operating on and
within the Earth throughout geologic time are the same laws and processes
operating today. Actualism is using the actual processes operating on Earth
today to interpret the past; not inventing unrecognized processes to explain the
past.
3.(2)-convergence zone: A linear area where plates collide and move closer
together. This is a zone earthquakes, volcanoes, mountain ranges and deep
ocean trenches.
4.(2)-core: The central zone or nucleus of Earth about 2,900 km (1,800 miles)
below the surface. The core is made mostly of iron and nickel and exists as a
solid inner zone (2450 km in diameter with temperatures up to 4300 degrees C or
7770 degrees F; similar in temperature to the surface of the Sun) surrounded by a
liquid outer shell. The Earth’s magnetic field originates within the liquid core,
where viscous movements of convections currents in the outer core generates
the magnetic field.
5.(2)-crust: The outermost layer of the lithosphere, composed of relatively lowdensity materials. The continental crust (granitic) has lower density than the
oceanic crust (basaltic).
6.(2)-divergence zone: A linear zone formed where plates pull apart, as at a
spreading center (ridge).
7.(2)-ductile: Behavior of material whereby stress causes permanent flow or
strain. Ductility is the ability to change shape markedly without breaking
(fracture): “plastic” behavior.
8.(2)-elastic: Behavior of material whereby stress causes deformation that is
recoverable; when stress stops, the material returns to its original state (if stress
greater than the yield strength of brittle material it can fracture). Pulling on a
rubber band is an example where if you let go before it snaps, it returns to its
original state.
9.(2)-epicenter: The point on the surface of the Earth directly above a fault
movement (i.e., earthquake location).
10.(2)-hot-spot: A place on Earth where a plume of magma has risen upward from
the mantle (i.e., a mantle plume!) and through a plate to reach the surface. This
happens, for example, at the Hawaiian and Galapagos Islands and creates a chain
of islands with the islands becoming progressively older away from the hot spot.
This is evidence of plate motion and can determine plate velocity and direction
over hot spot.
11.(2)-igneous rock: Rock formed by the solidification (crystallization) of magma
or lava. Granite and basalt are igneous rock; granite=continental crust, plutonic
rock from magma, less dense than basalt; basalt=oceanic curst, volcanic rock
from lava, more dense than granite (so oceanic lithosphere subducts and is
recycled).
12(2)-lithosphere: The outer rigid shell of the Earth that lies above the
asthenosphere and below the atmosphere and hydrosphere. The lithosphere is
comprised of the crust (oceanic and continental) and the upper, rigid mantle.
13.(2)-mantle: The largest zone of the Earth, comprising 83% by volume and 67%
by mass.
14.(2)-oldest rock and mineral: The oldest mineral is a zircon (sand grain) dated
at 4.37 billion years old from a sandstone in western Australia; the oldest rock is
dated at 4.055 billion years old from northwest Canada. Compare this to the
oldest seafloor rock that is 200 million years old (remember the seafloor is
continually recycled). The age of the Earth has to be older than the oldest rocks
and minerals, and is about 4.6 billion (4,600 million) years old.
15.(2)-Pangaea: A supercontinent that existed during Late Paleozoic time when all
the continents were unified into a single landmass.
16.(2)-plume: An arm of magma rising upward from the mantle. Not necessarily
liquid, can be solid rock.
17.(2)-radioactivity: The breakdown of unstable atomic nuclei by emission of
particles or radiation and energy is released. Source of energy keeping Earth’s
interior hot. The early Earth was transformed by this heat along with impact and
gravitational energy.
18.(2)-ridge: A volcanic mountain range that lies along the spreading centers on
the floors of the oceans.
19.(2)-seafloor spreading: Where tectonic plates pull apart, magma wells up and
solidifies to create volcanic mountains, which in turn are pulled apart as new
ocean floor.
20.(2)-strain and stress: Stress: external forces acting on masses or along
surfaces; forces include shear, tension and compression. Strain: A change in the
form or size of a body due to external forces.
21.(2)-subduction and trench: The process of lithospheric plate descending
beneath another one. Trenches mark the downgoing edges of subducting plates
and are narrow and elongate troughs where ocean water can be more than twice
its normal depth. The older, colder OCEANIC (only oceanic lithosphere subducts)
plate subducts beneath either a continental plate or younger, warmer oceanic
plate. For example, check out where the Pacific plate is created and destroyed
(where are the ridges and trenches? Transforms?).
22.(2)-plate tectonics and tectonic cycle: New lithosphere forms at oceanic
volcanic ridges, the lithospheric plates (a piece of the lithosphere that move a top
the asthenosphere; there are a dozen large plates and many smaller ones) spread
apart to open ocean basins, and then the oceanic plates are reabsorbed into the
mantle at subduction zones (marked by trenches at Earth’s surface). Plate
tectonics is the description of the movements of plates and the effects of plate
formation (at ridges), collision (at convergent zones), subduction (at convergent
zones) and slide past (at transform or strike-slip zones). The typical time for a
complete plate-tectonic cycle is in excess of 250 million years.
23.(2)-transform fault: A strike-slip fault that connects the ends of two offset
segments of plate edges, such as spreading centers or subduction zones. The
San Andreas Fault is a transform plate boundary and a right-lateral, strike slip
fault. Most movement is horizontal displacement of the Earth’s crust.
24.(3)-amplitude: The maximum displacement or height of a wave crest or depth
of a trough.
25.(3)-body wave: Seismic wave that travels through the body of the Earth-for
example, P and S-waves.
26.(3)-cross section: A two-dimensional drawing showing features in the vertical
plane, as in a canyon wall, road cut or mine.
27.(3)-dip: The angle of inclination measured in degrees from the horizontal.
28.(3)-dip-slip fault: Fault where most of the movement is either up or down
(vertical) in response to pushing or pulling.
29.(3)-fault: A fracture or belt of fractures in rock where two sides move past each
other. The most common cause of earthquakes is sudden movements along
faults.
30.(3)-footwall: The underlying side or block of a fault. (rock that lies beneath the
fault plane).
31.(3)-hangingwall: The overlying side or block of a fault (rock that lies above the
fault plane).
32.(3)-hypocenter (focus) and epicenter: The initial portion of a fault that moved
to generate an earthquake. Hypocenters are below the ground surface;
epicenters are above them and on the Earth’s surface.
33.(3)-law of original horizontality: Sediments are deposited in nearly horizontal
layers.
34.(3)-law of superposition: In a sequence of sedimentary rock layers, the oldest
layer is at the base, and ages are progressively younger toward the top.
35.(3)-magnitude: An assessment of the size of an event. Magnitude scales exist
for earthquakes, volcanic eruptions, hurricanes and tornadoes. For earthquakes,
magnitudes are calculated based on the energy released and are used to
compare earthquakes. The largest earthquake ever recorded by a seismograph
occurred during 1960 in Chile (9.5 magnitude).
36.(3)-mainshock: The largest earthquake in a sequence, preceded by foreshocks
and followed by aftershocks.
37.(3)-normal fault: A dip-slip fault in which the upper fault block (hanging wall)
has moved downward in response to tensional (pull-apart) stresses.
38.(3)-P (primary)-wave: The first seismic wave (body wave) to reach a
seismometer. Movement is by alternating push-pull pulses that travel through
solid, liquid and gas.
39.(3)-reverse fault: A dip-slip fault where the upper fault block (hanging wall) has
moved upward in response to compressional stresses.
40.(3)-right-lateral fault: A strike-slip fault where most of the displacement is
toward the right hand of a person straddling the fault. The San Andreas is a rightlateral strike slip fault (AND a transform plate boundary).
41.(3)-S(secondary)-wave: Second seismic wave (body wave) to arrive at the
seismometer. Movement occurs by shearing particles at right angles to the
travel path. S-waves move through solids only, and stop at the core/mantle
boundary! Why? Think about it.
42.(3)-strike: The compass bearing of the trend of a rock layer as viewed in the
horizontal plane.
43.(3)-strike-slip fault: Fault in which most of the movement is horizontal or slidepast in character. The San Andreas Fault in California is a transform plate
boundary between the Pacific and North American Plates AND it is also a rightlateral, strike slip fault, more than 800 miles long!
44.(3)-surface wave: A class of seismic waves that travel along the surface onlyfor example, Love and Rayleigh waves. These create most of the destruction
during seisms. These waves travel the slowest through rock.
45.(3)-wavelength: The distance between two successive peaks, or troughs, in
seismic waves or ocean waves.
46.(4)-liquefaction: The temporary transformation of water-saturated, loose
sediment into a fluid; typically caused by seismic waves. Example occurred in
the Marina District during the World Series earthquake of 1989.
47.(4)-rift: The valley created at a pull-apart zone. Term commonly describes the
valley that occurs along the axis of the volcanic mountain ranges where seafloor
spreading occurs. Make sure to read and understand the geologic processes
happening where we live; rifting of continental crust and development of a
spreading center that opened the Gulf of California beginning about 5.5 million
years ago-Baja torn from North American plate and piggybacked onto the Pacific
plate; read Chapter 4 beginning on page 82 and bottom of page 95 for more.
48.(4)-seismic-gap method: Earthquakes are expected next along those fault
segments that have not moved for the longest time.
49.(8)-fetch: The length of water surface the wind blows across to create waves or
lake-effect snow.
50.(8)-rogue wave: An unusually tall wave created when several wave systems
briefly and locally combine their energies.
51.(8)-seiche: An oscillating wave on a lake or landlocked sea that varies in
period from a few minutes to several hours. Pronounced saysh.
TEST 1