GEO 1013 Exam 2

Rock

Common, naturally occurring assemblage of at least 1 mineral, compacted/consolidated

Problems with rock definition

Obsidian (glassy volcanic rock)

Coal (sedimentary rock made of organic material)

Intrusive igneous rock

rock that cools under the crust, slower so allows more crystals to grow

Intrusive silica content high to low

Granite, diorite, gabbro

Extrusive igneous rock

rock that cools above the crust, cools very fast so fine grained crystals

Extrusive silica content high to low

rhyolite, andesite, basalt

Basaltic Lava

flows ready and fast, oceanic crust

Andesitic Lava

medium silica content, sticky, smooth peanut butter, can plug up and explode

Rhyolitic Lava

more complex silicate, crunchy peanut butter

Ejecta

ash and bomb, forms tuffs and breccias

Flows

hot expanding gas lifts density flow of ejecta

Pahoehoe

ropy lava that spreads in sheets and forms "skin", close to vent

Aa

blocky, less gasses so more viscous, farther from vent

Aphanitic

crystals too small for human eye

Phaneritic

mineral crystals large enough to be viewed unaided

Porphyry

large grained crystals in fine grained mixture

Rock formed at crust

Rhyolite

large igneous province (LIP)

Layers of flood basalts, 1 event can erupt as much lava as the ocean ridge system's annual output

Shape of LIP

Mantle plume, head, tail

LIP lava type

basaltic

What produces volcano change?

LIP, plates move but jet doesn't

Kileaua eruption length

65M years or more b/c subduction zone eats away

Ocean crust layers

Magma, Peridotite, Gabbro, Sheeted Basalt (dikes)

Differential melting/cooling

crystals settle out of magma layer, forming peridotite layer

Fissure Eruption

Highly fluid basalt flows readily away from vent, forming widespread layers

Ocean-ocean magma source

ocean crust and sediments

Continent-ocean magma source

mix of oceanic and continental crust and sediments

Fluid-induced melting

Ocean layer subducted, trapping water that heats up and melts overlying plate when released

Shield volcanoes

Fluid basalt (low silica content), gentle slope, large diameter, many many layers

Shield volcanoes examples

Mauna Kea, Mauna Loa, Iceland

Cindercones

Formed by pyroclastic fragments, steep and symmetrical small cone, no flowing lava

Cindercone example

Cerro Negro

Pyroclastic material

stuff that gets shot up in the air by the volcano

Composite cones/Stratovolcanoes

"typical" volcano, steep sided profile, snow, erosion resistant, lava and pyroclastic material, sheet dikes form and add stability, andesitic/basaltic lava

Stratovolcano examples

Mt. St. Helens, Mt. Vesuvius

Caldera

collapsed, evacuated magma chamber; steep-walled; circular; 40+ km diameter; gas comes up through fractures and then the ground collapses in

Caldera Example

Yellowstone (3)

Pyroclastic Flows

column of pyroclastic materials and gas fall to ground; Nuee ardente (glowing cloud); hot, fast, and far reaching; 30-200 m/s

Ash flow tuff

post flow the ash may weld/compact into a solid mass

Tuff example

Yosemite's Long Valley (Bishop Tuff)

Ash flow example

Mt. Vesuvius

Regional prediction

areas most likely

- subduction zones

- spreading centers

- hot spots

Violence

related to crustal domain

- continental (granitic/intermediate) - more violent

- basaltic - tend to be less violent

Short-term prediction

looking for time and place of eruption

- changes in shape

- earthquake swarms

- gas/ash emission

- temperature anomalies

Volcanoes and global cooling

ash and sulfur clouds reach high altitudes, reflecting solar radiation

Global cooling example

Pinatubo, 1991; solar radiation reaching Earth declined by 2-4%

Volcanoes and global warming

Eruption releases carbon dioxide gases, warming the earth

Global warming example

Permian extinction, 225 mya; 90% marine species and 65% reptile and amphibians, siberian flood basalts

Weathering

A major geologic process in the rock cycle that shapes the Earth's surface and converts all kinds of rocks into sediment and forming soil

Erosion and Transport

Processes that loosen and transport soil and rock downhill/downwind/downstream

Chemical Weathering

decomposition of rock whereby one mineral species is changed into another through chemical reaction

Mechanical Weathering

physical disintegration or degradation of rock without a change in composition

Controls on Weathering

Parent rock, Climate (rainfall and temperature), duration of exposure, presence of soil (positive feedback)

Mechanical Weathering Environment

arid and very cold climates, high mountainous areas

Chemical Weathering Environment

humid and tropical climates, low plains areas

Chemical weathering factors

Presence of water, temperature, surface area of mineral, mineral chemistry (stability)

Carbonic Acid weathering

CO2 from soil air, acts on both carbonate and silicate minerals

Oxidation

Mafic materials in 'reduced' state in subsurface oxidize when in near-surface Earth conditions, oxidation causes strain in mineral's crystal lattice, promoting breakdown

Pressure release fracturing

formerly buried rocks expand when uncovered

Frost wedging

water in cracks expands when frozen

Abrasion

rock particles moving in contact wear each other away

Organic activity

roots

Thermal expansion/contraction

minerals expand an contract when heated by the sun but at diff rates, causing mechanical weathering

Exfoliation

Concentric rock layers fracture and become detached from granite outcrop

Talus slope

Slope of rocks that fell from cliff

Selective weathering

Sediments require diff energy levels to be moved, heavier ones stay low and lighter ones can be carried higher

Spall

Rock breaks off in shells due to heat

Mass Wasting

downslope movement of Earth material under influence of gravity; landslide

Landslide causes

steep slope, type of rock and orientation of rock layers, nature of unconsolidated material, water and vegetation, earthquakes and volcanoes

Angle of repose

Maximum slope that can be maintained by a specific material, depends on type of material and water content (ie. drizzle art)

Flow

landslide where particles move independent of each other

Creep

slow movement, often of unconsolidated sediment (soil creep); land surface moves faster than deeper layers, so objects start to tilt

Debris flow

more than 1/2 the particles larger than sand sized, speed varies

Earth/mud flow

movement of fine-grained particles and water

Slide

landslide where material moves as a coherent mass

Slump

downward slipping of Earth materials, usually involves a rotation on concave surface

Rockslide

generally rapid movement of detached bedrock

Fall

Landslide where material free falls, occurs on very steep slopes or cliffs

Scarp

Steep slope, line of cliffs/edge produced by mass wasting

Undercutting

waves, streams, or construction erodes base of rock until top falls

Madison River Slide

1959 near Yellowstone, triggered by EQ, 30 million cubic meters of rock, 24 killed

Gros Ventre Landslide

(1925) Rock avalanche, 38 million cubic meters of rock, formed 200x400 yd dam that failed in 1927, killing 6 ppl, largest known mass wasting other than volcanic eruptions

Mt. St. Helens Landslide

1980, eruption heat melted glaciers and snowfields which mixed with ash and soil to create mudflows

Mt. Baker & Mt. Rainier could be susceptible

La Conchita

"Dumbest town in America", slides in 1995 and 2005, rainfall and earthquakes a threat, no good options

Predicting & avoiding landslides

Commonly occur in same area, pattern of human settlement often doesn't consider hazard evaluation, add building codes and practices

Sedimentary Basins

Sediment accumulates in basins of at least 10,000 square km; rift, thermal subsidence (sag), and flexural

Rift Basin

deep, narrow, and long with thick successions of sedimentary rocks and igneous rocks; rift develops as crust thins, seafloor spreads and things are deposited

Thermal Subsidence Basin

Crust sags from weight of sediments and cooling of lithosphere, deposits buried and go through diagenesis, lithified into sedimentary rock

Flexural Basin

Ocean-Continent boundary, sediments fall into basin

Lake/river sediments

Large (course-grained) sediments fall from mountain, mountain and lake high energy

Desert lake sediments

Fine grains, water evaporates

Meandering rivers

one channel winding across floodplain, sediment deposited on inside curve and outside curve erodes, changing river shape

Delta

river encounters standing body of water, sediment load dropped and sediments carried farther out depending on weight; deltaic deposit; distal edge; levee

Crevasse-Splay Deposits

2D Delta

Atoll

Coral reef encircling lagoon, foundation on topographically high structures on ocean floor, normally circular

Carbonate Deposition in atoll

Reef-building organisms precipitate carbonate as calcite aragonite (drop shells and such), sediment forms quicker than open ocean, and eventually carbonate platform grows w/ steep sides

Dunham's Classification of Carbonate Rocks

Ask questions: Depositional texture? Components bound? Carbonate mud? Mud/grain supported? > or < 10% grains?

Dunham's Classification of Carbonate Rocks Categories

Mudstone, Wackestone, Packstone, Grainstone, Boundstone, Crystalline

Eroding sand and silt

Takes more energy to erode/break them down but once it starts it can move at many velocities

Lithification

process in which sediments compact under pressure, expel connate fluids, and gradually become solid rock; process of porosity destruction through compaction and sedimentation