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Geology 103 2nd test
Volcanoes, Earthquakes & Tsunamis, Geological Strutures and Geological time
87
Geology
Undergraduate 1
11/11/2009

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Term
What factors influence a violent eruption?
Definition
Composition- more SiO2 means more viscosity, Temperature- more viscosity at lower temperatures, and gas(volatile) content- the more gas the more explosive.
Term
What has more SiO2 mafic or felsic rock?
Definition
Felsic rocks 70-75% SiO2 vs Mafic- about 50% or less.
Term
Viscosity
Definition
a Material's resistance to flow. Also the more viscous a magma is the more violent it's eruption will be.
Term
Volatiles
Definition
Gases held in the magma. As the near the surface the pressure lessens and the gases inside expand causing violence.
Term
Explosive vs Effusive eruptions
Definition
Explosive- are violent with high viscosity and a lot of trapped gas. Effusive- are passive with low viscosity and gas that escapes easily.
Term
Main types of volcanic structures
Definition
Shield, Cinder Cones, and Composite.
Term
Shield Volcanoes
Definition
From passive eruptions/lava flows. Huge structures with massive width to height ratios. They occur on other planets too.
Term
Cinder Cones
Definition
Can be explosive and passive, are short lived round piles of tephra from jets of lava that cool in mid-air and are then deposited around the flank of the volcano. have 45 degree angle of repose and erode very quickly.
Term
Composite
Definition
Usually explosive and can also be called a stratovolcano because they can blow rocks up into the stratosphere. They have steep slopes and are cone shaped. Often associated with layers of tehpra and lava flows. Tend to be associated with subduction and are very unstable.
Term
How did Mt. St. Helens erupt and when?
Definition
it gained a geotumor in 1980 and exploded violently.
Term
What are the two types of lava?
Definition
Pahoe hoe and A'a
Term
Pahoe hoe
Definition
smooth to the foot, has a smooth ropey appearance
Term
A'a
Definition
rough to the foot. This lava cascades forward and is rough, jumbled and jungly.
Term
Tephra
Definition
volcanic rock fragments
Term
Lava Fountains
Definition
A jet of lava sprayed into the air by the rapid formation and expansion of gas bubbles in the molten rock is called a lava fountain. Lava fountains erupt from isolated vents, along fissures , within active lava lakes , and from a lava tube when water gains access to the tube in a confined space.
Term
spatter cone
Definition
(driblet cone) Small (usually 5–20 m high), volcanic cone built from tephra blown out as clots of relatively fluid basaltic lava.
Term
Fissure eruptions
Definition
currents of "flaming" lava from a crack.
Term
Lava tubes
Definition
Lava can move in tubes. A "Skylight" is an opening into an underground tube system of lava.
Term
Plinian eruption
Definition
name for pliny the younger, conists of hot ash, rock fragments and gases being erupted from an explosive vent in a plum up to 100,000 ft or 5 miles high. The fragments can call at up to 100mph after the column collapses.
Term
Pyroclastic Flows
Definition
ash, gas and rock fragments. move at about 200 to 560 mph or 100 to 250m/second. Incredible destructive and leave deposits behind called "tuff"
Term
Tuff
Definition
pyroclastic flow deposits
Term
Ballistic Projectiles
Definition
also called bombs. Rocks are generally small but can be the size of a car or house. they are hot on the inside so they explode like a grenade on impact.
Term
Lahars
Definition
Have killed the most people over the last few 100 years. They are volcanic derived mudflows. rocks mixes with melted glaciers/snow caps or nearby bodies of water. They can be produced by a volcanic eruption or in between eruptions. they travel upwards of 60km/hr but are very viscous and impossible to swim out of.
Term
Tephra Fallout
Definition
Composed of ash, pumice, and rock fragments. fallout tends to pile up on buildings and cars causing damage and collapse. If breathed in it will coat your lungs with glass and cause asphyxiation.
Term
"Super-Volcanoes"
Definition
also called caldera forming eruptions. They are extremely large scale and erupt upwards of 1000 cubic kilometers. their fall deposits cover continents and the ash covers the globe causing global climate change. could end human existence.
Term
Caldera Formation
Definition
when an explosion causes collapse of the volcano into the magma chamber, can be up to 60km across is a cyclical process.
Term
Volcanoes linked to climate change
Definition
1815 volcano tamboro exploded and in 1816 it snowed in july in NE.
Term
Examples of super volcanoes
Definition
Crater lake, Oregon, Yellowstone, Krakatau, and Tambora(caused the snow).
Term
What are Earthquakes?
Definition
Vibrations of the ground created by the sudden release of energy accumulating in deformed rocks.
Term
Define: Focus
Definition
Also called the hypocenter this is the point of origin of an earthquake. aka where the rock actually begins to rupture or move.
Term
Epicenter
Definition
The point on the earth's surface directly above the focus.
Term
Name the different type of Seismic Waves of an Earthquake.
Definition
Body waves (P and S) and Surface waves (L and R)
Term
Primary waves
Definition
compression waves. They are the fastest at 4 mi/sec and travel through anything
Term
Secondary waves
Definition
Have vertical or horizontal motion. Travel at 2 mi/sec and do not move through liquid.
Term
Calculating distance from an earthquake.
Definition
Use the distance between the P and S waves. To locate the epicenter use 3 distance circles...
Term
R and L waves
Definition
Are surface waves. at 1.5mi/sec they are the slowest waves. L travel side to side and R travel up and down. together they have complex motion
Term
What determines a earthquakes strength?
Definition
Depth of the fault-deeper depth means it's less powerful. Strength of rock- stronger rocks are more powerful when the rupture. And the total amount of slip, the more the more powerful.
Term
Where do earthquakes occur?
Definition
Mostly along plate boundaries, though the can also occur along hot spots, and sometimes occur as intra-plate quakes.
Term
How do intra-plate quakes happen?
Definition
Ancient plate is reacctivated, there is a crustal weakness, isotacy or rebound after a glacier leaves and nearby magma.
Term
Isostacy
Definition
rebound after weight like a glacier leaves.
Term
How do we measure earthquakes?
Definition
With a sesmograph that puts out a sesmogram.
Term
The seismic shadow zone phenomenon
Definition
S waves don't go through liquid and P react wierdly through liquid. Both phenomenon create shadow zones so that you can't figure out where and earthquake is if you are within 103 degrees on either side of the earthquake.
Term
Earthquake scales
Definition
Mercalli and Richter
Term
Mercalli Scale
Definition
Qualitative (measure of the damage) ranges from I being the least damage to XII being the most damage and is based on relative levels of destruction.
Term
Richter Scale
Definition
Quantitative (Measured by energy). Is based on a scale of 1 to 10 and goes up logarithmically. Is based on the amplitude of the seismogram. Largest earthquake ever recorded was a 9.5. 2004 Tsunami was caused by a 9.3.
Term
Ground Motion
Definition
an earthquake hazard. can damage or collapse other buildings or structures.
Term
Uplift and subsidence
Definition
normal or reverse faults that cause structures to split. is another earthquake hazard.
Term
Scarp-
Definition
rock/cliff face that is visible after the ground drops down due to a fault.
Term
Landslides
Definition
another earthquake hazard.
Term
Liquefaction
Definition
Energy from an earthquake causes sediment to vibrate and behave like a liquid. caused water and other liquids to come to the surface.
Term
Fire
Definition
another earthquake hazard that can be caused when an earthquake breads a fuel line, gas pipe or the water pipes need to but out a fire.
Term
Travel time graph
Definition
Look it up!
Term
Tsunami
Definition
a crazy wave triggered by the ground shifting from an earthquake or by landslides/earthquakes nearby the water. Is a global phenomena. Can travel upwards to speeds of 500 mi/hr and can be 45 to 50 ft tall when it breaks on the shore. On the ocean you just get swells...
Term
Earthquake safety
Definition
can be achieve by seismic zoning rules, better building codes, stronger structures (that can accommodate seismic stresses), and taller columns which can sway better without breaking.
Term
2004 Tsunami
Definition
was a 9.3. killed over 200,000 people, displaced 1.69 million people.
Term
Tsunami safety
Definition
Education and better warning systems.
Term
How do rocks become deformed?
Definition
Stress(usually tectonic) leads to strain.
Term
Types of strain
Definition
Tension (Pulling apart), Compression (Pushing together), Shear (twisting or torsion).
Term
Types of deformation
Definition
Ductile (plastic smooth continuous), Brittle (sudden break), Elastic (deforms then returns back to it's orginal shape-ucommon!)
Term
Ductile Deformation
Definition
smooth and continuous leads to folding, shearing and stretching.
Term
Brittle deformation
Definition
Catastrophic and sudden. earthquakes are the result of brittle deformation. leads to faults.
Term
Types of faults
Definition
Reverse causes compression(head wall goes up), normal causes extension (head wall goes down), and strike-slip causes shearing.
Term
Folds
Definition
result when ductile rock undergoes compression
Term
Anticline
Definition
Convex or n-shaped fold.
Term
Syncline
Definition
Concave or u-shaped fold.
Term
Horizontal vs plunging fold.
Definition
Plunging fold plunges away from the horizontal and results in arcs on the surface. Horizontal folds have straight lines at the surface.
Term
Dip-slip
Definition
Normal and reverse faults. Motion is vertical.
Term
Thrust Faults
Definition
Low angle reverse faults. Layers are thrust up and over other rocks.
Term
Right lateral vs left lateral.
Definition
Stand on one side of the fault and look across to the other side has the rock been offset to the right or the left.
Term
Domes
Definition
Broad circular or oval upward bulges of rock layers. Rock layers tilt / or outward from the center of the dome. forms uplift in the center and has oldest rocks in the center.
Term
Basin
Definition
circular or oval downward sag of rock layers. Rocks tilt \ away from center. form from subsistence or sinking of the center and have youngest rocks at the center.
Term
Strike
Definition
The direction of the intersection of a rock layer with the horizontal surface.
Term
Dip
Definition
the angle and direction at which the beds are incline from the horizontal. (always perpendicular to strike.
Term
Deep time
Definition
The vastness of the geological record. (earth is 4.6 billion years old)
Term
Relative vs Absolute dating
Definition
comparison vs specific number dating.
Term
Stratigraphic analysis
Definition
stratigraphic succession is chronological record of the geologic history of a region.
Term
Original horizontality
Definition
sediments are deposited as essential horizontal beds
Term
Superposition
Definition
In an undisturbed sequence the oldest rock is at the bottom and the younger stuff is on top.
Term
Law of inclusions
Definition
rocks containing the inclusion is younger than the enclosed piece of rock.
Term
Cross-cutting relations
Definition
what ever is cutting is younger than what ever is cut or offset is older.
Term
Baked contact
Definition
thermal metamorphism occurs when country rock is invaded by a plutonic igneous intrusion. The backed rock is thus older.
Term
Unconformaties
Definition
indicate missing time in geological record from erosion or nondepositon.
Term
Disconformity
Definition
between relatively parallel strata.
Term
Nonconformity
Definition
between sedimentary rock and non-sed rock.
Term
angular unconformity
Definition
between non parallel strata.
Term
Fossils as timepieces
Definition
prevalent fossils may be used as index fossils or markers in stratigraphy.
Term
Radiometric dating
Definition
calculated ratio of parent isotopes to daughter isotopes. Needs a closed system. Is great for igneous rocks, ok for metamorphic rocks (rest at metamorphism) and is awful for sed rocks.
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