Final Study Guide, Midterm 2 Study Guide, GEOL 105 MIDTERM CLASS NOTES

Barrier reefs

Barrier reefs border a shoreline and are separated from land by an expanse of water, creating a lagoon of open, deep water between the reef and the shore

Desert streams

Usually seasonal, prone to flash flooding

Solar output

varies over long term (billions of years).

Main agent of erosion on coastlines

wave erosion

Wave-cut platform

A bench or shelf along a shore at sea level, cut by wave erosion

Tombolo

A deposition landform in which an island is attached to the mainland by a narrow piece of land such as a spit or bar. Related to longshore drift.

Turbidity current

A downslope movement of dense, sediment filled water created when sand and mud on the continental shelf and slope and dislodged and thrown into suspension

Valley glaciers

A glacier confined to a mountain valley, previously a stream valley

Oceanic heat conveyor

A global flow of warm surface water heads into the North Atlantic, becoming salty by evaporation in the tropics. As it cools, it sinks, and forms a cold salty current at depth that flows into the Southern Ocean and the Pacific. This current plays a major role in redistributing heat

Ice shelves

A large, flat mass of floating ice that form where glacial ice flows into bays and that extends seaward from the coast but remains attached to the land on one or more sides. (Once they've disintegrated they melt. Certain amount of ice turns into certain amount of water but doesn't affect sea level. Ice floating so it's displacing it's own mass of water—so when it turns into water it fills the displaced water so there's no change. Melting ice shelves and melting icebergs does not affect sea level. Melting ice cap does affect sea level but not where the ice comes into the ocean in the first place)

Barrier island

A low, elongate ridge of sand that parallels the coast

Hadley Cell

A tropical atmospheric circulation that features air rising near the equator, flowing poleward at 10-15 kilometers above the surface, descending in the subtropics, and then flowing equatorward near the surface

Ice sheets

A very large, thick mass of glacial ice flowing outward in all directions from one or more centers

Main causes of climatic variability

Albedo, greenhouse factor, global heat transport by ocean currents, orbital variations (Milankovich cycles), solar output

Time scales of climactic variability

Albedo: Time scales: sub-annual to hundreds of ky Greenhouse: decades to many millions of years ENSO: roughly decadal Orbital variations: 22-211 ky Solar output: long term (billions of years)

El Niño - Southern Oscillation

An approximately decadal oscillation of equatorial warm water in the Pacific. Affects global wind and precipitation patterns, and disrupts fisheries and agriculture. Time scales may be sub-decadal, to >10 my as a result of continental drift.

Sea-stack

An isolated mass of rock standing just off-shore, produced by wave erosion of a headland

Effect of longshore drift on man-made structures

As longshore drifts deposit, remove, and redeposit sand, they can destroy manmade structures built on the coastline. e.g. lighthouses have to be moved several times because the channels shifted constantly

Neap tides

At half moon tides are weakest

Spring tides

At new moon and full moon, tides are strongest

What causes desert climates

Atmospheric high pressure zones due to global air circulation patterns (Hadley cells) and continentality (distance from oceans). They associated with warm air that rises in the downwelling part of a Hadley convection cell

Sand spit

Beach landform found off coasts or lake shores by the process of longshore drift by longshore currents

Cause of seasonality

Because of the obliquity of the Earth's axis to the plane of its orbit around the sun, climatic zones migrate northward or southward with the seasons.

Upswash and backswash

Breaking waves produce an upswash and a backslash. The upswash is stronger than the backswash. Waves therefore transport coarser material up the beach, and carry finer material offshore

Abyssal plain

Broad areas of the deep ocean at depths of 5-6 km. Mainly clastic sediment up to several km thick on oceanic crust. Sediment deposited by turbidity currents.

Main types of sediment found on continental shelves

Clastic or carbonate dominated

Longitudinal (seif) dunes

Crests lie parallel to prevailing wind direction. Form when winds oscillate in direction with the seasons

Transverse dunes

Crests lie perpendicular to prevailing wind direction. Form when sand is abundant and winds unidirectional. Common in coastal environments.

What drives convection

Density contrasts which are caused by temperature contrasts. Hot air rises (lower density than cold air, hot air expands)

Pediment

Desert erosion produces steep mountain fronts that retreat and leave a flat eroded surface

Internal drainage (deserts)

Deserts generally do not have integrated fluvial systems. Internal drainage common. Water ends up in playa lakes.

What factors controls the pattern of ocean currents

Driven by convection and by wind, and are diverted by the Coriolis force. They are also strongly constrained by the continents.

How does El Niño - Southern Oscillation Work

During normal years, warm surface waters pool in the western tropical Pacific. During this event, the warm waters shift eastward.

What produces Milankovitch cycles

Earth's orbit is elliptical. Sun and Moon exert torque on equatorial bulge, which causes precession: axis rotates every 22 ky. Other planets attract Earth Orbital ellipticity varies every 100 ky. Tilt of Earth's axis varies by about 3° every 41 ky

Playa lakes

Ephemeral shallow lakes with evaporite deposits/Shallow seasonal lake formed in a desert environment

Internal structure of a sand dune

Eroded on upwind and deposited on downwind side, but the internal structure doesn't get affected

Foram

Forams grow shells of CaCO3 Forams put on 'heavy' isotope coats because. Ice sheets are light, so oceans are heavy (H2O molecules exchange oxygen with CO3-2). At lower temperatures, forams prefer to take CO3-2 molecules with heavy isotopes

How does an atoll form

Formed from ocean-island volcanoes by subsidence of the ocean floor

What characteristic erosional and depositional features are produced by running water in desert environments

Forms steep-sided canyons in the mountains. Deposits alluvial fans, dissected by washes (channels with vertical sides and flat bottoms)

Sea ice

Frozen seawater that is associated with polar regions. The area covered by sea ice expands in winter and shrinks in the summer

Accumulation

Glacial budget above snow line

Ablation

Glacial budget melting, calving or formation of ice shelves, sublimation

What is the frequency of tides

High tide every 12 hours 40 minutes on average

What factors combine to make a storm surge

Hurricanes and tropical storms produce powerful waves and heavy rain. Wind and breaking waves may cause water to pile up against a shore line. Low pressure in the storm center can cause a storm surge. May be accentuated by winds and high tides.

Longshore drift

If waves are oblique to the beach, they transport sediment along the beach

Global heat budget

Incoming solar radiation is balanced by out- going radiation from the Earth's surface. Outgoing radiation has a longer wavelength (and lower energy) than solar radiation

Barchan dune

Isolated crescent-shaped dunes with points downwind. Form when sand supply is limited and winds unidirectional. Common in rocky deserts.

Windblown sand

Mainly quartz: other minerals are rapidly abraded. Sand grains are rounded and frosted. Very well sorted

The main characteristics of wind-born sediment

Mainly quartz: other minerals are rapidly abraded. Sand grains are rounded. Wind-blown sand is very well sorted

What are the characteristic features of the sediment turbidity currents deposit

Medium-grained sediment (due to the medium-energy transport mechanism)

What sort of sediment is likely to be deposited on a mid-ocean ridge

Pelagic sediment

What characteristic features does internal drainage produce

Playa lakes

Sandy beaches

Produced by fair weather waves

Pebbly beaches

Produced by storm waves

How are tides produced

Produced by the gravitational fields of the moon and the sun

Why is a certain type of sediment likely to be deposited on a mid-ocean ridge

Protected from clastic sediment, so accumulate Carbonate ooze above carbonate compensation depth becomes pelagic limestone and siliceous ooze below CCD becomes chert. Very slow rates of deposition

Tidal flat

Redeposition of sediment by tides creates these

How are global climatic zones controlled by the patterns of atmospheric circulation

Rising air near the equator condenses to form clouds and rain, descending air in the mid-latitudes causes clear skies and desert climates

Factors that control which type forms

Sand abundance, wind direction, environment type

Features produced by wind

Sand dunes, desert streams, pediments

How sand moves over a sand-dune

Sand is eroded from the windward side of the dune. Sand is deposited on the lee side.

How is it possible to get such a thickness of sediment on a continental shelf

Sediment wedge built out on a passive (rifted) margin. Water depth < 200 m

Continental shelf

Sediment wedge built out on a passive (rifted) margin. Water depth < 200 m. Sediment thickness up to 15 km. May be clastic or carbonate dominated. They are virtually horizontal (not sloped continuously and gently down into the deep ocean basins)

Milankovitch cycles

Serbian Engineer and Mathematician predicted changes in solar radiation due to variations in Earth's orbital parameters. Time scales of 22-110 ky. Records from temperature proxies such as oxygen isotopes reveal this cyclicity

Continental shelf/slope/etc

Shelf--slope--rise--abyssal plane

What characteristic coastal features are produced by sediment transport

Spits, bars, barrier islands, lagoons and deltas

How do turbidity currents initiate

Submarine currents. Mixture of sediment and water. Higher density than water. Turbulent flow keeps sediment in suspension.

Storm surge

The abnormal rise of the sea along a shore as a result of strong winds

Insolation

The amount of solar energy received per unit area is least at the poles, greatest at the equator. This contrast drives convective circulation in the atmosphere and the oceans, which transports heat from the equator to the poles.

What factors control whether glaciers and ice sheets advance or retreat

The glacial budget controls whether the glacier is advancing, retreating or remaining stationary. The glacial budget is the balance between the accumulation at the upper end of the glacier and loss at the lower end

Snow line

The height of the snow line (above which snow does not melt completely) varies with latitude. Poles: permanent ice at elevations b/w sea level and a few hundred meters above

Where do we find the main deserts in the world

The main deserts in the world are found in Antartica, North Africa (Sahara), Western Asia (Arabian desert) and Central Asia (Gobi desert). Clear band of deserts on all the continents in the northern hemisphere around 30 degrees N, also similarly in Southern hemisphere around 30 degrees south, controlled by climactic zones.

Movement of glaciers

The motion of glaciers involves plastic flow of solid crystalline ice. Warm-based glaciers move in part by sliding on their base. Glaciers can flow up the slope of their base. Glaciers can only flow downwards in the direction of their surface slope

Global vegetation

The pattern of global vegetation is a proxy for global climate. Note heavy vegetation in the tropics, the light colored desert areas in latitudes around 30°N and S, and the more vegetated areas at latitudes around 60°N and S

What processes allow ice in glaciers and ice sheets to move

The plastic flow is movement within the ice due to ice's molecular composition as the bonds between layers are weaker than those within each layer allowing the layers to slide over one another. Basal slip is the second process in which meltwater acts as lubricant and enables the ice mass to slip along the ground over rock

Coriolis effect

This effect interacts with the Haldey circulation to create patterns of easterly and westerly winds

What features do tideal currents form

Tidal flats

Tideal currents

Tides create strong currents in shallow and restricted waters, which change direction twice each day. Tidal currents scour channels and transport sediment in shallow water

How does the flow of ice compare with the flow of water in a river

Unlike streamflow, glacial movement is not obvious. Similar to the flow of water in river, the ice in the glacier does not move at an equal rate; rate of flow is greatest in the center of the glacier

Deep sea trenches

Up to 11 km deep, located along subduction zones. Trap sediment from volcanic arcs and active continental margins. Thick sequences of sediment deposited by turbidity currents. Currents flow along trench for many hundreds of km. Trench sediment is subducted and accreted to form an accretionary wedge

How thick can the sediment pile get on a continental shelf

Up to 15km thickness

Continental slope and rise

Up to 5 km high with slopes of a few degrees. Commonly cut by submarine canyons. Little sediment deposition.

Post-glacial rebound

Uplift of Baltic region in meters in the past 5000 years related to melting of the ice sheet 10,000 years ago.

What drives atmospheric circulation

Variations in insolation cause convection cells on a global scale

Facts about atmospheric circulation

Warm moist air rises near the equator. Cool dry air descends at about 30 degrees latitude N and S. Moist air rises at about 50-60 degrees latitude N and S. Rising air in the Hadley circulation is associated with clouds and rain

Gulf Stream

Warm, salty water that flows up north in the Atlantic and cools as it gets there, getting denser. Because of convection.

What factors control the budget of glaciers and ice sheets

Warming and cooling trends, ablation, increases and decreases in snowfall

Most important agent of erosion in deserts

Water

How is sediment transported in coastal environments

Waves and currents distribute sediments

How do submarine canyons form

When a seaward extension of a valley was cut on the continental shelf during a time when sea level was lower or when turbidity currents carved a canyon into the outer continental shelf

External structure of a sand dune

Wind moves sand, it hops along from its former position by erosion to its future position with deposition. Sand is eroded from the windward side of the dune. Sand is deposited on the lee side.

Deflation

Wind tends to remove sand and dust from desert soils

Desert pavement

Wind tends to remove sand and dust from desert soils, leaving behind this

Three main types of dune

barchan dunes, transverse dune, longitudinal (seif) dunes

Greenhouse factor

depends on H2O, CO2, CH4 content of atmosphere. Time scales of decades to many millions of years

Waves are agents of

erosion, sediment transport, and deposition

Albedo

ice cover, dust, cloud cover can change. Time scales: sub- annual to hundreds of ky.

Ventifacts

pebbles shaped by natural sandblasting

Marine terrace

relatively flat, horizontal, slightly inclined surface of marine origin. An old abrasion platform which has been lifted out of the sphere of wave activity