Geol 110 Unit 2

Mt. St. Helens

Violently erupted in 1980 in Pacific NW blowing down trees and losing 1350 ft of elevation

Viscous

Resistance to flow

What makes violent eruptions?

Si composition, lower temperature, and trapped gas

All three factors play into each other

Effusive volcanic eruption

Mafic, basalt, Hawaii

Erupting constantly

Trapped gas but low viscosity causing lava fountains

Rocks: vesicular basalt (scoria)

Aa and Pahoehoe flow

Aa flow

Jagged, blocky, very sharp

Pahoehoe flow

smooth, ropy, texture

Explosive volcanic eruption

Associated with more intermediate and felsic lava

Composition leads to high viscosity which leads to explosive eruption

High amounts of dissolved gas: H₂O, CO₂, SO₂, H₂S

Have eruption column

Eruption column

Huge column of smoke/gas formed when dissolved gas escapes

Forms pyroclastic rocks

Pyroclastic rocks

Rocks formed from hot ash cloud

Classified based on size of pyroclastic material: volcanic ash, lapilli, volcanic bombs

Dissolved gas

under pressure gas dissolved, once pressure released gas forms bubbles and escapes liquid

Types of volcanoes

Shield volcanoes, and stratovolcanoes

Shield volcanoes

Form from mafic lava (basalt)

Very large laterally and vertically

low relief/slope

forms from the repetitive eruption and flattening of basaltic lava

Ex. Hawaii

Tallest mountain from base to height

Mauna Loa

Dome volcano

Tallest mountain in the solar system

Olympus Mons

Shield volcano

Stratovolcanoes

Forms from intermediate lava (andesite)

High verticality but not as large laterally

Steeper sides

Form from intermediate lava flow making cone shape then pyroclastic layer on top repeated

Ex. any south American volcano and Pacific NW Mountains

Volcanic environmental hazards

Pyroclastic flow, lahar, ash cloud, volcanic gas emissions, and tsunamis

Pyroclastic flow

occur at stratovolcanoes

eruptive column made of hot ash and gas state rock

dense, comes “flowing” down the mountain

Deadly

Lahar

Both strato and shield volcanoes

rising magma melts snow causing water to flood carrying ash and debris in massive landslide

Ash cloud

Mainly strato

Some pyroclastic rocks too fin to settle, gets into atmosphere as ash cloud

impacts air travel, agricultural and repiratory problems

Volcanic gas emissions

Both shield and strato

Emit more CO₂ and SO₂ than all humans combined

May have helped start climate change and extinctions in the past

Can also have localized deaths due to desner SO₂

Tsunamis

Underwater/coastal volcanoes can cause tsunamis if they release a lot of materials

Alfred Wegener

1915 proposed theory of continental drift

Didn’t provide mechanism for movement so was disregarded

Continental drift

continents moving over time, not stable, once part of Pangaea

Evidence for continental drift

FIt: continents look like they fit together

Identical fossils across fit

Identical and unique mountain ranges across fit

Rocks in current location could not have formed in that environment of deposition (swamp rocks in Appalachia and glacial rocks in Africa)

What technology developed out of WWII

Nuclear fision — gave info on isotopic dating

Sonar — sea floor mapping

Mid Ocean Ridges (MOR)

Semi linear chain of mountains down center of ocean. Generally follow shape of coastlines. Lava erupting in the center with symmetrically older rock on either side of ridge

Mechanism of continental drift

Sea floor spreading

found 1950s-60s

Theory of plate tectonics

Earth’s crust made up of series of individual plates that are constantly moving and interacting

Low movement (few-10 cm per year)

Interactions at boundaries responsible for geologic events

Types of crust

Oceanic crust (10 km thick) basaltic, dense

Continental crust (40 km), granitic, less dense

Asthenosphere

Fluid toothpaste layer plates sit ontop of (semi-fluid)

Lithosphere

Crust and upper mantle (solid/rigid) that makes up plates

Types of plate boundaries

Divergent, convergent, and transform

Divergent plate boundaries

Plates move apart and new seafloor is created

Mostly in the ocean, MOR

Oceanic vs oceanic

Continental vs continental only in East African Rift Valley

Mainly small earthquakes and volcanoes

East African Rift Valley

Continental vs continental divergent plate boundary

continents splitting creating valley

severe volcanoes and earthquakes

Convergent plate boundaries

Plates move together, can create mountain belts or recycle oceanic lithosphere

Can be oceanic vs oceanic, oceanic vs continental, or continental vs continental

Major earthquakes and volcanoes

What slab subducts at convergent plate boundaries

The oceanic slab (in o vs o the older oceanic slab) because of its greater density

Oceanic vs oceanic convergent plate boundaries

Japan and pacific isles

Older slab denser due to it being hydrated

Oceanic vs continental convergent plate boundaries

West coast of America

Oceanic palte subducts

Continental vs Continental convergent plate boundaries

Himalayas and alps (rare)

Less subduction more one slab rafting over other

large plateau and mountains

few to no volcanoes

Transform plate boundaries

Plates grind past each other

mainly oceanic vs oceanic or oceanic vs continental

major earthquakes, no volcanoes

What causes plates to move and stop moving

Convection in the mantle

Earthquakes

Energy released in the Earth that leads to ground shaking

most common release is pressure between two blocks at palte boundary

energy builds up over time from palte movement (only at plate boundaries or past boundaries)

smaller earthquakes before and after

Fault

plane of breaking

seismometer

how we measure earthquake intensity and location

pen tip stays still while rest of earth moves

Primary waves (P)

compression waves that travel through all materials and travel very fast

Secondary waves (S)

Sheer waves that only travel through solid materials

while slower than p waves still pretty fast

Body waves

S and P waves

Surface waves

Travel in rock layers just below Earth’s surface

Occur when body waves reach Earth’s surface and propogate

Cause greatest destruction but travel the slowest

Earthquake detection

Time interval between P and S waves tell distance from Earthquake which can then be used to triangulate position of Earthquake

Earthquake intensity scales

Mercalli intensity scale and Richter magnitude scale

Measurements of earthquake size

Intensity: observing property damage to estimate amount of ground shaking

Magnitude: use data from seismograph

Mercalli intensity scale

Measures earthquake intensity based on observed damage

Sale from I to XII

I nothing really felt except in very specific circumstances

XII damage total, visible waves

Helpful for past earthquakes

Richter magnitude scale

Data driven, based on highest amplitude of seismograph

Logarithmic scale

Millions of small magnitude Earthquakes occur per year while maybe one high magnitude will occur per year

Earthquake destruction

Actual earth shaking doesn’t kill people, rather resulting secondary effects do.

Damage dependent on earthquake intensity as well as construction of buildings

Worst material for Earthquake buildings

Masonry

Best material for earthquake materials

Steel

Why do less developed countries typically have more deaths due to earthquakes

Buildings less codified and more often built from masonry resulting in greater damage and deaths

Liquefaction

When the soil turns to quicksand as a result of ground shaking

destroys buildings regardless of composition

Tsunamis

Earthquake in ocean forms a long wavelength but short amplitude wave on waters surface

Radiates away from epicenter at 100s of mph

Gets close to shore where it experiences more drag causing wavelength to shrink and amplitude to grow, pulling water away from shores

Total global water

oceans 96.5%, saline lakes and groundwater 1%, freshwater 2.5%

Total global freshwater

glaciers and ice sheets 68.6%, groundwater 30.1%, surface water 1.3%

Total global surface water

snow and ice 73.1%, lakes 20.1%, soil moisture 3.52%, swamps 2.53%, rivers .46%, biological water .22%, atmosphere .22%

Stream

Any water that flows in a channel regardless of size

River

Carries a substantial amount of water

Drainage basin/watershed

the area of land a stream drains

Can have drainage basins within drainage basins

divides

lines dividing drainage basins

sometimes visible as high ridge on mountains

sometimes hard to determine due to topography

Continental divide

a divide that splits a continent into different drainage basins

Rocky mountains in US

Drainage patterns

patterns of interconnected streams in an area

Types: dendritic, radial, rectangular, trellis

Dendritic drainage pattern

most common

uniform underlying material

Radial drainage pattern

typically forms on volcanic cones or domes

Ex. Adirondacks

Rectangular drainage pattern

bedrock is jointed or faulted

joints or cracks

trellis

bedrock consists of alternating bands of resistant and weak strata

ex. Pennsylvania area

factors effecting flow velocity

gradient and channel shape (wetted perimeter)

gradient

the slope of the stream

steeper gradients have more gravitational energy to drive channel flow

wetted perimeter

area where the river is in contact with the channel

most efficient channels have small wetted perimeter compared to cross sectional area

discharge

how much water is going through a certain point in a river at a single moment of time (ft³ or m³ per second)

measured by propeller in water that measures velocity

best measure of river size

river stage

height of water surface relative to a fixed point

measured by stilling well

Biggest US river

Mississippi river (#8 in world)

Biggest river globally

Amazon river

US Geological Survey (USGS)

measures velocity, discharge, and river stage across 7,500 rivers

gives flood warnings by measuring high stage water in tributaries

Headwaters

start of streams

high gradient, high channel roughness, low velocity

Mouth of streams

end of streams

high discharge and velocity, low slope, low channel roughness

Graph of sediment transportation

How is sediment transported

Dissolved load, suspended load, bed load

Dissolved load

sediment dissolved in water

Suspended load

Fine sediment transported in suspension

clay and silt

Bed load

sand, gravel, and boulders transported by sliding, skipping, or rolling along river bottom

Saltation

bed load transportation by bouncing

alluvial channels

braided and meandering channels

Braided channel

a complex network of converging and diverging channels that thread among numerous islands or gravel beds

form in mountains

large proportion of load is coarse material (bank material easily eroded and reworded)

Stream has high variable discharge

Meandering channel

streams transport suspended sediment in broad sweeping bends called meanders

form in flat areas

relatively deep channels generally transporting mud

Cut bank

where erosion occurs at outside of meander

High velocity

Point bar

where deposition occurs at inside of meander

low velocity

Oxbow lakes

form when erosion connections meandering stream sections and cuts of a meander

meander

broad sweeping bend of a river

flood plain

formed through meandering stream migrating over time

side to side energy flattens floodplain over time

flooding deposits clay making very nutrient rich soil

Natural levee

flooding deposits larger sediments on tip of river bank creating a natural levee due to drastic decrease of velocity upon flooding

sources used for freshwater consumption

75% surface water, 25% ground water