geology midterm 2

process that produces physical weathering

\-freeze/thaw

happens in cold climates - density change

water seeps into rock, freezes overnight, and melts making the crack bigger

\-growth of salt crystals

crystals put pressure on the rock

\-plant roots

roots can grow in cracks causing pressure

\-exfoliation

differential expansion due to heating and cooling in rock layers

weathering (definition and processes)

\-breakdown of rocks and minerals at the earth’s surface

\-allows erosion: movement of rock

\-weathering processes:

physical(mechanical): fragmentation of rock, no compositional change, just breaking the rock down

chemical: chemical reactions, changing the rocks chemical composition

Regolith

\-unconsolidated debris over bedrock and is found at the surface of earth and other planets

Soil

\-a part of the regolith that has undergone chemical weathering, contains organic matter, and can support life

* mineral breakdown (weathering) and transport takes place within soils

material transport (physical, chemical, and surface accumulation)

\-physical

* aided by biota - insects, worms, mammels, microorganisms

\-chemical

* leaching, precipitation

\-surface accumulation

* clays/dust, solutes, and organics

soils from distinct horizons acronym

O- Organic

A- Topsoil

E- Eluviated

B- Subsoil

C- Parent Material

R-Bedrock

CLORPT - acronym

climate, organisms, relief, parent material, time

* warm + wet = faster weathering and thicker soils
* tropical soil
* cold + dry = slower weathering and thinner soils
* desert and polar soils
* hot + dry or cold + wet = intermediate soil formation
* temperate soil

organisms that increase soil producion rates

\-plants

* roots, decaying vegetation - carbonic acid, production of organic acids

\-animals

* physical breakup, aeration, access by fluids

sedimentary rocks

\-sediments are the products of the physical and chemical weathering of rocks

\-weathering products are raw material

* fragments of parent rock
* minerals produced by chemical weathering such as clay and iron oxides
* ions dissolved in water

sedimentary rock categories

\-clastic

* formed from solid fragments (clasts)
* boulders, sand, gravel, clay

\-chemical

* precipitated from dissolved compounds
* the formation of calcite

sedimentary rock cycle (5 steps)

\-weathering

* hard rock is transformed to regolith/soil

\-erosion

* sediments are moved to their final resting place

\-depositon (sedimentation)

* particles settle as energy decreases

\-burial

* air and water are expelled and porosity decreases

\-diagenesis (lithification)

* physical/chemical changes turn sediments into rocks

conglomerates

* rounded clasts
* river transport
* clastic
* cemented together usually by silica, calcite, or iron oxide

breccia

* found at the base of hills (after physical weathering)
* streams (only short distances from origin)
* clastic type
* large-sharp angled fragments embedded in a fine-grain mix of smaller particles or mineral cement
* comes before conglomerate

clastic sedimentary rock tyoes

* categorized based on clast size and texture
* sandstone
* clastic consisting of sand-sized clasts
* sandstone is 25 percent of all sedimentary rocks
* quartz is most abundant followed by feldspar
* slitstone and mudstone
* clastic containing slit and clay materials
* mudstone is a shale if thinly layered
* rich in organic matter

sedimentary origin and texture

* if found near a source…
* poorly sorted, poorly rounded, less mature
* breccias
* if found further from a source…
* well sorted, well rounded, more mature

chemical sedimentary rocks

* chemical sediments form when dissolved ions and molecules combine into solid materials
* examples:
* when solid precipitates from an aqueous solution it has a chance of combining into a solid material such as a sedimentary rock

Messinian salinity crisis

* the mediterranean sea became partially dried up by looking at evaporite sediments and rock formations (6 million years ago)

types of metamorphic rock

* pressure related to depth
* example: prograde metamorphism of a shale protolith
* shale: layered sedimentary rock formed from mud
* prograde: increasing temperature from pressure
* leads to…
* shale → slate → schist → gneiss

metamorphic processes

* metamorphism is a transformation of a protolith to another rock
* caused by..
* heat, pressure, fluids
* can cause a change in mineralogy and change in texture
* size, shape of crystals in a rock
* alignment of crystals
* the alignment of crystals results from stress being applied to the rock
* pressure related to depth
* foliation

reverse thrust faults

* one block is pushed up
* fault line is at an angle
* compressional stress (pushed together)
* contraction

strike-slip transform faults

* fault plane nearly vertical
* blocks move horizontally
* shear strain

normal faults

* one block drops down
* fault plane at a steep angle
* extensional stress
* elongation

seismic waves

* vibrations in the rock generated by rupture along a fault
* propagated in all directions
* exact speed depends upon the nature of the wave
* two categories…
* body waves
* surface waves

p-waves

* primary
* seismic body wave that shakes the ground back and forth in the same direction and the opposite direction as the wave is moving
* travel faster than s waves

s-waves

* secondary
* transverse waves, meaning that the direction of the particle motion is perpendicular to the direction of wave propogation, and the main restoring force comes from shear stress
* travel slower than p waves

love waves

* produce entirely horizontal motion

rayleigh waves

* include both longitudinal and transverse motions that decrease exponentially in amplitude as distance from the surface increases

earthquake energy and epicenters

* different velocities of the p and s waves are used to locate earthquake epicenters
* p and s waves travel outwards from the region of the fault that ruptured
* p- waves arrive first at the seismometer, than s-waves
* proportional to the slip on the fault multiplied by the area of the fault surface that slips
* related to the total energy released by EQ

wadati-benioff zone

* a planar zone of seismicity corresponding with the down-going slab in a subduction zone

discovery of the earth’s liquid outer core

* p - waves and s - waves travel differently in the earth
* density, rigidity, and compressability affect wave movement
* seismic waves reflect and refract

moho discontinuity

* boundary between earth’s crust and the mantle
* defined by the distinct change in velocity of seismic waves as they pass through changing densities of rock
* lies within the lithosphere

vibrations from an EQ can trigger landslides based on…

* geology
* stability of rocks
* slope steepness
* hydrology
* waterlogged or dried out
* sediment does not have much strength
* meteorology (weather)
* affects hydrology

sand boils

* occurs naturally during an EQ
* a cone shaped deposit that formed during an EQ
* water pushes up through the sediments and causes the sediment to fracture
* begins to seep through and create sand boils
* associated with liquidfaction
* process of ground water to flow toward the surface due to seismic waves

case studies EQ hazards

* buildings were old - brick work collapsed
* haiti (2010)
* roof too heavy - couldn’t support
* EQ a trigger for conflicts
* strike-slip fault
* turkey/syria (2023)
* transform fault
* concrete not strong against high motion
* corruption charges - buildings not up to code

formation of coal

* special case of chemical sediment
* organic matter put under pressure and heat can either become oil and gas or coal
* comes from organic sediment from plants
* wood, bark, leaves, pollen, sometimes viable fossils
* can only form in low oxygen environments
* swamps or mires primarily
* leads to preservation in the following sequence…
* swamp muck → peat → lignite → bituminous coal → anthracite coal

anticline vs. syncline

* anticline: a ridge shaped fold of stratifed rock in which the strata slopes downward from the crest
* syncline: a fold of stratified rock in which the strata slopes downward
* the type of deformation is strongly rrelated to plate tectonic environment

coral reefs

* only form in the photic zone of shallow marine waters
* requires sunlight
* reef sediments accumulate as corals grow
* construction of carbonate platforms
* susidence of seafloor or rise of sea level
* attolls - reef islands with circular lagoons
* construction of carbonate platfroms on extinct volcanoes

plankton and the white cliffs of dover

* microscopic organisms that live near the ocean surface (photic zone)
* leads to chalk limestone units
* e.g., the white cliffs of dover

epicenter

* the point on the surface that is directly above the focus
* earthquake foci can be used to map out faults and fault lines

earthquake magnitude is measured by…

* richter scale or moment magnitude Mw

energy released within an earthquake

an M7.O quake releases 31.6 times more energy than an M6.0 quake or around 1,000 times more energy than a M5.0 quake

earthquake secondary hazard example

* earthquakes can create secondary hazards from volcanoes
* landslides, tsunamis, decompression of magma chamber (extreme cases)
* e.g., Mt St Helens, WA, 1980