Geol 3050 Exam 1 preparatory Notes

1-3-17
 March 20, 1980: 4.1 magnitude earthquake struck below Mt. St Helens. First warning
sign.
March 27: small explosion blew 250 ft hole in mountain. Released ash plume.
May 18: mag 5.1 earthquake shook Mt. St Helens. 57 people killed or missing.
 Volcanology: study of origin and ascent of magma through earth’s mantle, crust, and its
eruption at the surface.
 Volcano: vent in Earth’s surface through which magma and/or associated gases erupt.
 Stratosphere
Troposphere
Lithosphere
Asthenosphere
Mesosphere
 The location of volcanoes is determined by plate tectonics.
 Continental crust: silica rich, 30 – 70 km thick, above oceanic crust.
- Oceanic crust: iron and magnesium rich, silica poor, 7 km thick.
- Mantle: dense rock of iron and magnesium, less silica than crust.
o Upper mantle: 100 km thick, lithosphere
o Lower mantle
- Transition zone: very dense and ridged.
- Mesosphere: perovskite – (Mg, Fe) SiO. Iron, magnesium oxides with some
silica, denser and more ridged than upper mantle.
- Core: iron and nickel. Inner core: solid metal. Outer: molten metal.
 Divergent boundary: 2 plates move apart to make new sea floor. Spreading centers.
- Convergent boundary: subduction zones. Allochthonous terranes.
- Transform fault boundary: 2 plates move against each other without damage.
1-5-17
 Quartz is the most resilient mineral from volcanoes.
 Plate boundaries: rocks pulled, squeezed, or twisted. Breaking of rocks makes
earthquake.
 Faults: fractures in rocks that allow displacement to occur.
- Strike slip: horizontal displacement of rock.
- Dip slip: parallel to dip. Vertical.
- Normal: hanging wall moved down relative to foot wall.
- Reverse: hanging wall moved up relative to foot wall. Compressional stress.
 Earthquake: vibration of earth made by rapid release of energy.
- Focus: actual point of rock rupture.
- Epicenter: point above focus.
 Types of seismographs
- Horizontal ground motion
- Vertical ground motion

,  Types of seismic waves
- Body: travels through earth’s interior.
- Surface: travel along the outer part of earth.
 Needs at least 3 stations to triangulate exact location of earthquake.
1-10-17
Review (blue text: answers to exam questions)
 Blast zone 19 miles from Mt. St Helen: channelized blast zone.
 Harmonic tremors: indications on seismographs from movement of magma.
 Low angle reverse fault: thrust fault.
 P waves reach seismograph first.
 Offset: distance of movement across fault.
 Rupture length: length of break along fault during earthquake.
 2 measurements for earthquake size
- Magnitude: energy released at source.
- Intensity: how much damage it caused.
 Largest recording on Richter scale: 8.9. Largest recorded earthquake: 9.5 Chile (5-22-
1960).
- < 2.0 not felt by humans.
 Igneous rock: crystallization of magma.
- Granite, quartz, hornblende, feldspar.
 Mineral: naturally occurring inorganic solid with a definite and not fixed chemical
composition.
 Polymorph: chemical substance capable of crystallizing several distinct crystal forms.
 Bowen’s reaction series: scheme to show in order in which different minerals crystallize
during coding and progressive crystallization of magma.
 Magmatic differentiation: process of generating more than 1 rock type from a single
magma.
1-12-17
Review
 Volcanic basalt: pyroxene, calcium-rich feldspar.
 Garnet: a not common rock-forming mineral.
 Volcanic glass forms when lava is cooled rapidly from being ejected quickly from
volcano.
 Carbonatite: igneous rock with more than 50% carbonate mineral.
 Igneous activity found at plate margins and within plate itself (intraplate).
 At plate margins, igneous activity is associated with spreading centers and subduction
zones.
 Decompression melting occurs as the lithosphere is pulled apart.
 3-21-2010: volcanic eruption shot ash and molten lava into air. First major eruption in
nearly 200 years in Iceland.