GOL 105 Exam 3

Orogeny

A specific episode of orogenesis (mountain building).

What are all of the processes and forces involved in mountain building? In other words, how are mountains built?

Most orogenesis occurs along convergent plate boundaries, where compressional forces cause folding and faulting, thickening the crust vertically and shortening it horizontally. Mountains are built through tectonic activity, collisions and orogenesis.

What are the Earth effects of mountain building?

Geological Structures, Earthquakes, Seismic Waves

anticlines

Upward-arching folds in the Earth's crust where the OLDEST layers of rock are in the core of the fold.

synclines

A linear downfold in sedimentary strata; the opposite of anticline.

normal faults

A fault in which the rock above the fault plane has moved down relative to the rock below.

reverse faults

A fault in which the material above the fault plane moves up in relation to the material below.

horsts

an elongated, uplifted block of crust bounded by faults

grabens

A valley formed by the downward displacement of a fault-bounded block

sag ponds

pond caused by the collection of water from springs and/or runoff into sunken ground, resulting from the crushing of rock in an area of fault movement

right lateral strike slip fault

as you face the fault, the opposite side of the fault moves to the right

Because movement along the San Andreas Fault causes the crustal block on the opposite side of the fault to move to the right as you face the fault

left lateral strike slip fault

as you face the fault, the opposite side of the fault moves to the left

The Great Glen Fault in Scotland, which exhibits the opposite sense of displacement of the San Andreas Fault

What types of earth structures are formed by Compressive forces?

Folds, Anticlines, and synclines, reverse fault

What types of earth structures are formed by Shear forces?

Strike-slip Fault, sag pond

What types of earth structures are formed by Extensional forces?

Normal fault, Dip-slip fault, megathrust fault, horst, graben

Mercalli Intensity Scale

A 12-point scale developed to evaluate earthquake intensity, based on the amount of damage to various structures.

Earthquake Scales

Mercalli and Richter

What are the differences between the different earthquake "scales"?

Intensity (Mercalli) vs. Magnitude (Richter)
Intensity: Measurement of destructions
Magnitude: Measurement on seismograph

epicenter

The location on Earth's surface that lies directly above the focus of an earthquake.

focus

The point beneath Earth's surface where rock breaks under stress and causes an earthquake

hypocenter

The zone within Earth where rock displacement produces an earthquake.

fault plane

A break in a rock mass along which movement has occurred.

earthquake

Vibration of Earth produced by the rapid release of energy.

Richter Magnitude Scale

A scale of earthquake magnitude based on the amplitude of the largest seismic wave.

How do we locate earthquakes? Why do we need three great circles? What is the point at the center of a great circle when locating earthquakes?

The system for locating earthquake epicenters was developed by using seismograms from earthquakes whose epicenters could be easily pinpointed based on physical evidence. From these seismograms, travel-time graphs were constructed. Using the seismogram and the travel-time curve, we can determine the distance separating the recording station from the earthquake in three steps:

1. Using the seismogram, we determine the time interval between the arrival of the first P wave and the arrival of the first S wave
2. Using the travel-time graph, we find the location where the vertical separation between P and S curves is equal to the P-S time interval
3. From the position in step 2, we draw a vertical line to the horizontal axes and read the distance to the epicenter.

B. We need three great circles to use a method called triangulation which is used to find the direction of the waves (the epicenter)

C. Epicenter

The distance separating a recording station from an earthquake's epicenter can be determined by using the difference in arrival times between P and S waves. When the distances are known from three or more seismic stations, the epicenter can be located using a method called triangulation.

Earthquake cause

Caused by differential stress that gradually bends Earth's crust over tens to hundreds of years. Up to a point, frictional resistance along the fault keeps the rock from rupturing and slipping. Once that point is reached, the fault slips, allowing the bent rock to "spring back" to its original shape, generating an earthquake. The springing back is called elastic rebound.

Where do earthquakes occur in the US? Why is California at great risk? Where else within the US has experienced earthquakes?

Tsunamis are caused by

underwater earthquakes and volcanic eruptions

Tsunami

A giant wave usually caused by an earthquake beneath the ocean floor. The Japanese word for a seismic sea wave.

seismic wave

a wave of energy that travels through the Earth, away from an earthquake in all directions
generated by the slippage of a rock mass

Types of seismic waves

body waves and surface waves

Body waves

seismic waves that travel through the Earth's interior. P waves and S waves

Primary Waves (P-Waves)

Travel the fastest through rock material by causing particles in the rock to move back and forth , or vibrate, in the same direction as the waves are moving.

Seismic waves that involve alternating compression and expansion of the material through which they pass.

Secondary Waves (S Waves)

only travel through solids and temporarily change the shape, but not the volume of the material they pass through; move slower than P waves

Seismic waves that involve oscillation perpendicular to the direction of propagation.

Surface Waves

seismic waves that travel along the Earth's surface.

there are two types of surface waves. One type causes Earth's surface and anything resting on it to move up and down, much as ocean swells toss a ship
The second type of surface wave causes Earth's surface to move from side to side. This motion is particularly damaging to the foundations of structures

artesian well

a well created by drilling a hole into a confined aquifer

artesian spring

a spring whose water flows from a crack in the cap rock over the aquifer

Here groundwater may reach the surface by rising along a natural fracture such as a fault rather than through an artificially produced hole. In deserts, artesian springs are sometimes responsible for creating oases

mass wasting

the downslope movement of rock, regolith, and soil under the direct influence of gravity

temporary base level

The level of a lake, resistant rock layer, or any other base level that stands above sea level.

ultimate base level

Sea level; the lowest level to which stream erosion could lower the land.

drainage basin

The land area that contributes water to a stream. Also called a watershed.

gradient

The slope of a stream, generally expressed as the vertical drop over a fixed distance.

discharge

The quantity of water in a stream that passes a given point in a period of time.

gaining stream

A stream that gains water from the inflow of groundwater through the streambed.

losing stream

A stream that loses water to the groundwater system by outflow through the streambed.

capacity

The total amount of sediment that a stream is able to transport.

competence

A measure of the largest particle a stream can transport; a factor dependent on velocity.

Types of Aquifers

confined and unconfined

Aquifer

A body of rock or sediment that stores groundwater and allows the flow of groundwater.
Rock or sediment through which groundwater moves easily

Aquiclude

Impermeable layer that is a barrier to groundwater; such as silt, clay, and shale.
A localized zone of saturation above the main water table, created by an impermeable layer

Aquitard

A slab of impervious surface at the bottom of an aquifer that does not allow water to go through
An impermeable bed that hinders or prevents groundwater movement.

confined aquifer

A groundwater storage area trapped between two impermeable layers of rock.
An aquifer that has impermeable layers (aquitards) both above and below.

unconfined aquifer

An aquifer made of porous rock covered by soil, which water can easily flow into and out of.

meanders

A looplike bend in the course of a stream

meander neck

Meanders may become so severe that point bars become narrow isthmus of land separating the portions of the meander

meander cutoff

A new, shorter channel across the narrow neck of a meander.

oxbow lake

A curved lake that is created when a stream cuts off a meander.

cut bank

the area of active erosion on the outside of a meander

point bar

a crescent-shaped accumulation of sand and gravel deposited on the inside of a meander

levees

Barriers composed of sediments made on either side of a river due to flooding.

yazoo tributary

A tributary that flows parallel to the main stream because a natural levee is present.

braided channel

A stream channel that is interwoven with other stream channels. Such channels form where a large portion of a stream's sediment load consists of coarse material (sand and gravel) and the stream has a highly variable discharge.

Where along a straight stream channel is the water moving the fastest?

Near the surface and in the middle.

Where along a meander bend is water moving the fastest?

Water will tend to flow fastest along the outside bend of a meander

Where along a meander bend is erosion occurring?

Cut bank. Erosion will take place on the outer parts of the meander bends where the velocity of the stream is highest

Where along a meander bend is deposition occurring?

Point Bars. Sediment deposition will occur along the inner meander bends where the velocity is low.

Sinkhole

A depression produced in a region where soluble rock has been removed by groundwater. Also known as a sink

"In 90% of sinkhole cases, water saturating the ground is the main trigger, known as Karst processes." "Sinkholes happen when a layer of rock underneath the ground is dissolved by water.

Cavern

A naturally formed underground chamber or series of chambers most commonly produced by solution activity in limestone.

Caves are formed by the dissolution of limestone.

How does groundwater get into the ground?

The Earth's surface is permeable, which means that it takes in water in like a sponge. Water gets into an aquifer from the land surface. Typically, precipitation falling onto the Earth's surface soaks into the ground and flows down to the water table.

How is carbonic acid made?

accumulation of CO2 bind with water
the reaction of carbon dioxide dissolved in water.

For example, carbon dioxide in the atmosphere dissolves in raindrops, forming carbonic acid. As acidic rainwater soaks into the ground, carbon dioxide in the soil may increase the acidity of the weathering solution.

Where is carbonic acid made?

Carbonic acid is present in blood in the human body. It is formed in the human body when water gets dissolved with carbon dioxide. It is also present in rainwater, calcite, fermentation, coal, groundwater, meteors, volcanoes, amino acids, proteins, oceans, plants, erythrocytes, sulphur deposits, salts, and caves.

Liquefaction

The transformation of a stable soil into a fluid that is often unable to support buildings or other structures
The process by which an earthquake's violent movement suddenly turns loose soil into liquid mud

Mass wasting types

slump, rockslide, debris slide, debris avalanche, debris flow, mudflow, lahar, earthflow

slump, rockslide, debris flow, earthflow, creep, solifluction

slump

The downward slipping of a mass of rock or unconsolidated material moving as a unit along a curved surface.

A slump is a distinctive and common form of mass movement in which coherent blocks of material move downhill on a spoon-shaped slip surface. Slumps are often marked by curved scarps that open up at their tops. They are frequently triggered by overstepping, such as that caused by stream erosion of a valley wall.

rockslide

The rapid slide of a mass of rock downslope, along planes of weakness.

Rockslides are rapid mass movement events in which a coherent block of rock slides downhill along a planar surface. Often this is a preexisting structure such as a joint or a bedding plane. Situations where these surfaces dip into a valley at an angle are especially dangerous.

debris slide

A type of rockslide consisting of largely unconsolidated rock debris.

debris avalanche

One of the fastest and most destructive types of rockslides consisting of unconsolidated rock fragments.

debris flow

A flow of soil and regolith that contains a large amount of water. Most common in semiarid mountainous regions and on the slopes of some volcanoes.

Debris flows occur when unconsolidated soil or regolith becomes saturated with water and moves downhill in a slurry, picking up other objects (trees, houses, livestock) along the way. Varieties of debris flow include mudflows, which are dominated by small particle sizes, and lahars, which involve volcanic materials. Debris flows can move quickly—up to 30 kilometers (nearly 20 miles) per hour.

mudflow

A flow of soil and regolith that contains a large amount of water. Most common in semiarid mountainous regions and on the slopes of some volcanoes.

lahar

A debris flow on the slopes of a volcano that results when unstable layers of ash and debris become saturated and flow downslope, usually following stream channels.

earthflow

The downslope movement of water-saturated, clay-rich sediment. Most characteristic of humid regions

Earthflow is characterized by a similar loss of coherence between grains in unconsolidated material, but it is much slower than debris flow. Typically, sites of earthflow show an uphill scarp and a lobe of viscous soil on the downhill side.

How are mass wasting events classified?

1. Type of material (rock, earth, mud, debris, ice, etc.)
2. Type of movement (fall, slide, flow)
3. Rate of movement (rapid, slow)

Different types of mass movement are generally classified based on the type of material involved, the kind of motion displayed, and the velocity of the movement.

creep

The slow downhill movement of soil and regolith.

Creep is a very slow form of mass movement that is both important and widespread. It occurs when freezing (or wetting) causes soil particles to be pushed out away from the slope, only to drop down to a lower position following thawing (or drying).

solifluction

The slow, downslope flow of water-saturated materials common to permafrost area

Solifluction is the gradual flow of a saturated surface layer that is underlain by an impermeable zone. In arctic regions, the impermeable zone is permafrost.

What are all the features associated with a meandering stream?

cut banks, point bars, cut off, an oxbow lake

Streams that transport much of their load in suspension generally move in sweeping bends called meanders. These streams flow in relatively deep, smooth channels and primarily transport mud (silt and clay), sand, and occasionally fine gravel.

What's the difference between gaining and losing stream?

Gaining: A stream that gains water from the inflow of groundwater through the streambed.

Losing: A stream that loses water to the groundwater system by outflow through the streambed.

Gaining streams have water flowing year‐round or for extended periods such as wet seasons, whereas losing streams tend to have flow only in response to water‐input events like rainfall and otherwise have no flow.

A stream may gain water from the inflow of groundwater through the streambed. Such a stream is called a gaining stream. For this to occur, the elevation of the water table must be higher than the level of the surface of the stream. Conversely, a losing stream loses water to the groundwater system by outflow through the streambed. For a losing stream to form, the water table must sit lower than the surface of the stream.

Porosity

the volume of open spaces in rock or soil

Permeability

a measure of a material's ability to transmit water

Which types of sediments/rocks are porous but not permeable?

Clay

Which types of sediments/rocks are permeable but not porous?

Gravel

Which types of sediments/rocks are porous and permeable?

Gravel and sand

What controls river discharge?

The discharge of a river system changes over time because of variations in the amount of precipitation received by the watershed.

Studies show that when discharge increases, the width, depth, and flow velocity of the channel all increase predictably. As we saw earlier, when the size of the channel increases, proportionally less water is in contact with the bed and banks of the channel. This reduces friction, which acts to retard the flow, resulting in an increase in the rate of streamflow.

cone of depression

A cone-shaped depression in the water table immediately surrounding a well.

A cone of depression forms when...

water is withdrawn faster than it can be replaced

cones of depression are found...

A cone of depression occurs in an aquifer when groundwater is pumped from a well. In an unconfined aquifer, this is an actual depression of the water levels. In confined aquifers, the cone of depression is a reduction in the pressure head surrounding the pumped well.

"cone of depression" negative effects

If there is sufficient drawdown, the cone of depression might encompass a large enough area to cause neighboring wells to go dry.

flood

an overflowing of a large amount of water beyond its normal confines, especially over what is normally dry land.

100 year flood

probability in a given year for a flood of that size has a 1 in 100 chance of occurring in any year. 1% chance.

500 year flood

expected flood event that has a probability of 1 in 500 of occurring in any given year. 2% chance

Where do earthquakes occur in the US?

Western America, especially along the coast