Geology quiz #2

Cinder cones

Are predominately comprised of a large pile of loose cinders that formed during Strombolian eruptions

Ash fall

Ash falling from an eruption column or ash cloud

Partial melting

When magma forms in the mantle, only a portion of the rock melts

metamorphic grade

-metamorphism occurs across a range of pressure + temperature -metamorphic grade increases as pressure and temperature increases

How does magma form?

1. Add energy 2. Reduce pressure 3. Add volatiles

How do rocks metamorphose?

1. Add heat 2. Increase pressure 3. Apply stress

Metamorphic Environments

1. Contact (thermal) metamorphism- occurs adjacent to igneous intrusions or lava flows where there is a temperature increase 2.Regional metamorphism- occurs across broad regions in response to tectonic plate collisions. These collisions lead to major mountain-building events, called orogenies. -orogeny: the process of mountain formation especially by folding of the earth's crust. Entire mountain ranges with intensely deformed rocks result.

cinder cone eruptions

1. Gas-charged eruption- lava is blown violently into the air and breaks into small fragments that solidify and fall as cinders 2. Cones form- cinders all back around the vent and accumulate to build a cone 3. Lava flows- after excess gases have largely dissipated, molten rock quietly effuses from the base of the cinder cone.

Classifying igneous rocks

1. Texture- size of mineral grains 2. Composition- type of minerals present Mineral size is related to cooling rate: -large mineral grains = slower the cooling rate -smaller mineral grains = faster cooling rate

Magma formation at subduction zones

1. Volatiles, predominantly H2O, is released from subducting slab 2. Volatiles are added to mantle rock above the slab. 3. This lowers the melting temperature of mantle rock and melting occurs

Formation of detrital sedimentary rocks

1. Weathering of a preexisting rock 2. Transportation of erosion of sediment by wind and water 3. Deposition of eroded sediments 4. Litification - processed by which deposited particles become a rock a. Compaction - compacting particles via burial b. Cementation - fluids percolating through the open spaces (pores) Precipitate minerals. This fills in the pores and cements the sediments together

Pyroclastic flow

A hot, dry, fast-moving (20 to > 200 mph) and high-density mixture of ash, pumice, rock fragments and gas.

Lahar

A mudflow caused by a volcanic eruption.

Protolith

A parent rock that is transformed into a new rock

Craton

A part of the earth's crust that has remained stable, and has been little deformed for a prolonged period.

facies

A rock unit with specified characteristics that result from the depositional environment in which the rock formed

Fumarole

A steam vent that forms when modest amounts of groundwater come into contact with hot rocks underground, are turned to steam and forced out of the vent

Plinian eruption

A sustained, explosive eruption that forms a high, let-like column of pumice and ash in the atmosphere.

Resurgent dome

A volcanic done that rises due to upward movement of magma after a crater or caldera form

Geyser

An intermittent fountain of hot water in which hot columns of water are ejected with great force. Process 1. Water in subsurface chamber is heated 2. At some point, the pressure becomes too great & a small amount of water is forced out at the surface. 3. That loss of water reduced the pressure & it boils instantly. Steam erupts from the geyser. 4. Cool ground water seeps into empty chambers and the process starts anew

Shield volcanoes are shaped like:

An inverted warrior's shield Ex. Hawaii volcanoes NP

Tephra

Catch-all term for solid material of all sizes explosively ejected from a volcano into the atmosphere

Biochemical sedimentary rocks

Chert- cryptocrystalline quartz that formed from the microscopic skeletons of silica-secreting organisms Limestone- calcium carbonate that formed from: Shell debris, reefs, and carbonate mud

Caldera

Circular depressions that form when LARGE explosive eruptions cause the collapse of the center of a volcano -collapse of the ground forms a depression happens when large volumes of magma are removed from a shallow magma chamber - calderas are different from craters, which are smaller, circular depressions created primarily by explosive excavation during eruptions

Organic sedimentary rocks

Coal- Forms from compaction and heating of plant debris that accumulated in a swamp like environment Oil/shale- Rich in algae when deposited - burial and heating converted the algae into kerogens that remains trapped in the shale

Dome volcano

Compositionally similar to a composite volcano -have a lower gas content -smaller than composite volcanoes -have steel sides -high Si, low Fe & Mg -rock type: rhyolite

Cinder cone volcano

Compositionally similar to a shield volcano -have high gas content -smaller than shield volcanoes -have steep sides -low Si, high Fe & Mg -rock type: basalt

Mount Rainer NP, Washington

Considered the "most dangerous" volcano in the lower 48 states because glaciers on the summit would produce lahars.

Crater lake NP, Oregon

Crater lake is one of the cascades volcanoes The explosive eruption of Mount Mazama left behind a caldera that filled with water forming crater lake.

sedimentary rock types

Detrital- composed of mineral and/or rock fragments Biochemical- composed of shell fragments cemented with organic mud Chemical- material that precipitates (crystallizes) from water Organic- carbon-rich remains of plants and/or animal

Chemical sedimentary rocks

Evaporites- form from the evaporation of water rich in soluble ions Travertine- calcium carbonate minerals that precipitate from ground water or spring water Dolomite- dolomite typically begins as limestone. Chemical reactions with magnesium rich fluids add mg to the rock. chemical composition is altered and crystal structure is re-organized to form dolomite

composite volcano (stratovolcano)

Explosive eruptions produce: -narrow cones -steeply sloping sides -high Si, low Fe & Mg -rock type: andesite and rhyolite The are composed of alternating layers of tephra and lava from many eruptions Generally andesite to rhyolite in composition

Igneous composition

Felsic rocks- rich in Si and poor in Fe and Mg. Dark rock Intermediate rocks- composed of both dark and light-colored minerals (salt and pepper texture) Mafic rocks- Rich in Fe and Mg and poor in Si. Light rock Ultra Mafic rocks- extremely rich in Fe and Mg. Has an olive green color.

Foliated metamorphic rocks

Foliation- preferred orientations (layering or banding)

Yellowstone caldera

Formed 640,000 years ago producing a lot of ash The recurrence interval is ~650,000 years Statistically this volcano is due to erupt

mudpot

Forms when steam rises through groundwater that has dissolved the surrounding rocks into clay.

Ash

Fragments less than 2mm in diameter of lava or rock blasted into the air by volcanic explosions.

Primary classification of sedimentary rocks

Grain size- use for primary naming. The rock name is based on the green size of the sediment it was derive from and can range from gravel-sand-silt-clay/mud

Hot springs

Ground water is heated by magma below the surface and flows to the surface forming hot springs

Lassen NP, California

Has dome volcanoes

Devils tower NM, Wyoming

It's a volcanic neck; the conduit that feeds a volcano. The surrounding, less resistant, rocks were dropped away leaving devils tower behind.

Assimilation

Magma composition mixes with host rock

Igneous rocks-solidified molten rocks Molten rock is called: Where they solidly they are called:

Magma- below the earth's surface Lava- on the surface Extrusive- at the earth's surface Intrusive- below the earth's surface

Mount St. Helen's erupted catastrophically on

May 18th, 1980

Grand Canyon NP

Numerous transgressions and regression's are recorded in the rocks of the Grand Canyon

Examples of shield volcanoes

Pahoehoe and A'a'

Pyroclastic

Pertaining to fragmented (clastic) rock material formed by a volcanic explosion or ejection from a volcanic vent.

Primary textures of igneous rocks

Phaneritic- large grain size due to slow cooling below earth's surface. "Intrusive" or "plutonic" Aphanitic- fine-grained crystals due to fast cooling at/near earth's surface. "Extrusive" or "volcanic"

Secondary textures of igneous rocks

Porphyritic- large and small mineral grains coexist (chocolate-chip cookie texture). Two-stage cooling: first slow, then fast Vesicular- Swiss cheese texture, has large holes Frothy- "spongy" texture Glassy- cooling was so fast that crystals don't have time to grow Fragmental- consists of fragments of igneous rock

How does heat/pressure/stress metamorphose rock?

Recrystallization- shape and size of grains is changed without changing the composition of the grains New mineral growth Preferred orientations- metamorphic processes acting upon a rock may result in the alignment of minerals grains into preferred orientations

Migmatites

Rocks that are only partially molten

Type of volcano chart

Shield volcano- passive eruptive style, oceanic crust/mantle melt source, low silica content, low viscosity, basalt rock, Hawaii Composite (stratovolcano)- explosive eruption style, continental crust melt source, high silica content, high viscosity, andesite/rhyolite rock, Mount St. Helens

Cinders

Solidified lava fragments about 1 cm in diameter. They were erupted as fragmented blobs of lava, solidified in the air, and fall back into a pile forming the cinder cone.

Columnar joint

The columnar shape that basalt forms as lava cools and contracts, forming cracks. Once the crack develops it continues to grow. The growth is perpendicular to the surface of the flow

Craton exposed by weathering and erosion:

This requires a large amount of erosion because the rocks formed very deep in earth's crust

Shield volcano

passive eruptions produce: -broad cones -gentle sloping sides -low Si, high Fe & Mg -rock type: basalt

Crystalline basement rocks

the metamorphic and igneous rocks of the craton