Geology Exam #3

What are deserts?

characterized by a lack of precipitation & high evaporation rates

Desert Characteristics

• rainfall is unpredictable

• when rain does fall it is intense & of short duration

• location is determined by patterns of atmospheric circulation

What causes wind?

differential heating of the Earths surface

Important Things to Note About Wind

• proximity of deserts to windy environments are key for shaping the landscape

• Earth spinning all by itself is not cause by winds

Lower Atmospheric Circulation with Hadley Cell & Coriolis Effect

• Top Polar Easteries & Northeast Trade Winds

  • winds move southwest

• Top Mid-Latitude Westerlies

  • winds move northeast

• Bottom Polar Easteries & Southeast Trade Winds

  • winds move northwest

• Bottom Mid-Latitude Westerlies

  • winds move southwest

Desert Location Determined by Patterns of Atmospheric Circulation

• warmest at equator

• coldest deserts at top or bottom

Trade Winds

• 0-30 degrees

• air moves toward the equator but curves west

• east to west

• descending cool, dry air

• rising warm, moist air

Westerlies

• 30-60 degrees

• air moves towards the poles but curves east

• west to east

• rising warm, moist air

Polar Easterlies

• 60-90 degrees

• cold air flows outward & curves west

• east to west

• descending cool, dry air

Wet Winds

• wind that blows over oceans picks up water vapor

• rising air cools and can’t hold as much moisture

• warm air holds moisture

Dry Winds

• winds that come from continents

• sinking air warms and holds moisture

• cold air holds little moisture

What are the types of deserts?

• Subtropical

  • Sahara

• Continental Interior

  • Gobi Desert

• Rainshadow Deserts

  • Mohabbi Desert

How does wind transport sediments?

• Saltation

• Suspension

• Creep

What is saltation?

a specific way wind moves sand-sized particles along the ground; bouncing motion

• lifted off the ground

• travels short distance through air

• falls back down

What is suspension?

when very fine particles (dust or silt) are lifted & carried in the air for long distances

• wind picks up tiny particles from surface

• turbulence keeps them from settling

• travel high in the atmosphere & can move hundreds-thousands of miles

What is creep?

movement of the largest & heaviest sediment particles

• instead of being lifted in the air particles roll or slide along surface

• move slowly & stay in constant contact with ground

• pushed by wind indirectly

Is the wind efficient in moving sediments around?

least efficient

What are the types of wind erosion?

• deflation

• abrasion

What is deflation?

removal of loose material by wind

What is abrasion?

near surface effect caused by impact of saltating sand grains

What are the types of sand dunes?

• barchan

• parabolic

• longitudinal

• transverse

What are barchan sand dunes?

• crescent shaped

• tips point downwind

• in areas that are flat & dry

• little vegetation

• limited supply of sand

• constant wind direction

What are parabolic sand dunes?

• crescent shaped

• tips point upwind

• commonly in coastal areas with strong onshore winds

• abundant sand

• partial cover of vegetation

What are longitudinal sand dunes?

• long, parallel ridges

• aligned parallel to the wind direction

• winds generally converge from slightly different directions

• 30-100 m high; 100 km long

What are transverse sand dunes?

• long ridges

• perpendicular to the wind direction

• sand seas

• 200 m high; 3 km wide

What is desertification?

a type of land degradation in which a relatively dry land region becomes increasingly arid, typically losing its bodies of water as well as vegatation & wildlife

What is desertification caused by?

• climate change

• human activities

What are waves created by?

wind energy

What are swells?

storm waves

What is wavelength?

distance between crests

What is wave height?

the vertical distance between the trough and crest

What is a period?

time required for one wavelength to pass a set point

What is a wavebase?

½ of wavelength

What is wave refraction?

waves bend as they encounter shorelines

What is the overall goal of wave refraction?

to make shoreline flat & smooth

What are tides created by?

gravitational attraction between the Earth and Moon that pulls water toward the moon

What are spring tides?

moon and sun line up twice a month to produce higher than average tides

What are neap tides?

when the moon is in the 1st and 3rd quarter, the moon and sun are working against each other to produce lower than average tides

What are tidal surges?

abnormal rises in sea level caused by strong storms not by normal daily tides

What are the types of tidal currents?

• flood tides

• ebb tides

What are rip currents?

strong, narrow channels of water that flow away from the shore pulling water back out to sea

What are the features of a shoreline?

• beaches

• offshore, foreshore, backshore

• erosion & coastal forms

• depositional coastal forms

What are the types of erosion & coastal forms?

• stacks

• wave-cut terraces

• sandy beaches

What are the types of depositional coastal forms?

• spits

• barrier islands

What are stacks?

tall isolated pillars of rock standing just offshore formed by the erosion of cliffs

What are wave-cut terraces?

flat, gently sloping rock surfaces found at the base of coastal cliffs created by wave erosion over time

What are sandy beaches?

coastal landforms made of loose sand that has been deposited along the shoreline

What are spits?

long, narrow ridges of sand or shingle that extend out from the coastline into the sea, formed by deposition

What are barrier islands?

long, narrow islands made of sand that run parallel to the mainland coast formed by deposition of sediment by waves, tides, & currents

What are the types of continental margins?

• passive

• active

What are passive continental margins?

coastal regions where a continent meets the ocean but is not located at an active plate boundary

• no subduction zones

What are active continental margins?

coastal regions where a continent meets the ocean at a plate boundary

• tectonically active

What is the order of shoreline features? (closest to furthest from shore)

• coastal plain

• continental shelf

• continental slope

• continental rise

• sea floor

Coastal Plain

a broad, flat or gently sloping area of land next to the ocean formed by long-term deposition of sediments and/or a retreating shoreline

Continental Shelf

the shallow, gently sloping underwater edge of a continent that extends from the shoreline out to the deep ocean

• broad, flat plains of sand & mud

• shelf-slope break

Continental Slope

the steeply sloping zone that connects the continental shelf to the deep ocean floor

Continental Rise

gently sloping zone at the base of the continental slope

What is at the seafloor?

• abyssal plain

• seamounts, volcanoes, & guyots

• reefs

What is the abyssal plain?

the very flat, deep part of the ocean floor found beyond the continental rise

What are glaciers?

systems of ice originating on land through the accumulation and recrystallization of snow

What are the 3 types of glaciers?

• valley glaciers

• continental glaciers

• piedmont glaciers

What are valley glaciers?

• originates high on a mountain and moves downward through preexisting valleys

• cirque glaciers are special types of valley glaciers that occupt an erosional feature that is cut into bedrock and is bowl shaped

What are continental glaciers?

a slow-moving ice sheet that resembles a giant dome several thousand meters thick in the center and sloping down toward sea level on all sides

What are piedmont glaciers?

found at the foot of a mountain & occur when valley glaciers come out of mountains and join the foot of a mountain

Where do glaciers form?

in areas where winter snowfall exceeds summer melting

• zone of accumulation

Describe the process of glaciers forming

• does not require year-round snowfall, only cold enough to have snow exist through the summer

• the weight of accumulating snow compress lower layers into glacial ice

• as the ice accumulates it begins to flow

• the glacier also loses ice

  • zone of ablation

What does the balance of ice ablation & accumulation have to do with whether the glacier is standing still or shrinking?

• if the glacier is standing still accumulation = ablation

  • glacier is neither gaining nor losing overfall mass

• if the glacier is shrinking ablation > accumulation

  • more ice is melting or breaking off than being replaced

How do glaciers move?

• basal sliding

• creep

• ice flow due to crevasses

What is basal sliding?

the process where a glacier moves by slipping over the ground beneath it

What is creep?

the slow internal deformation of ice where the glacier moves by the ice itself changing shape under pressure rather than sliding over the ground

Valley Glaciers

long, narrow glaciers that form in mountain valleys and flow downhill like slow-moving rivers of ice

Continental Glaciers

very large, thick masses of ice that cover vast areas of land including entire regions or continents

What are the features of glacier systems?

• striations

• erratics

• drumlins

• eskers

• kettle lakes

• moraines

• outwash plain

What are striations?

long, parallel scratches or grooves cut into bedrock by a moving glacier

What are erratics?

large rocks or boulders that have been transported and deposited by a glacier, often far from their original location

What are drumlins?

elongated, smooth, hill-shaped mounds of glacial till that were formed under moving ice sheets

What are eskers?

long, winding ridges of sand and gravel deposited by meltwater streams flowing beneath a glacier

What are kettle lakes?

small, often circular lakes that form when blocks of ice left behind by a retreating glacier melt and leave a depression in the ground

What are moraines?

accumulations of unsorted sediment called till that are deposited directly by a glacier

What are outwash plains?

broad, flat areas of sand and gravel deposited by meltwater flowing out from a glacier

What are the types of valley glaciers?

• aretes

• cirque

• horn

• hanging valley

• truncated spurs

• terminus

• moraines

  • lateral moraine

  • medial moraine

What is a river?

• a stream runoff is an important geolgic agent

• erodes, transports, & deposits ion and sediments

• sculpts landscapes

• transfers mass from continents to oceans basins

What is the anatomy of a river system?

• head or headwaters

• trunk or channel

• mouth

What is a head or headwater?

the uppermost part of a river where it begins

What is a trunk or channel?

the primary river channel that carries water from tributaries toward the river’s mouth

What is a mouth?

the end point of a river where it flows into a larger body of water

Are rivers effective in changing landscapes?

• yes because they are always moving

• erosion & deposition never stop

• landscapes are changing relatively quickly in response to moving water

What are stream valleys?

elongated low-lying areas of land carved out by the long-term erosion of a river or stream

What are floodplains?

flat, low-lying areas of land next to a river that are regularly flooded when the river overflows its banks

How does erosion occur?

• abrasion

• chemical & physical weathering

• undercutting

What is abrasion?

a process of erosion where rock and sediment carried by wind, water, or ice scrape, & grind against a surface, wearing it away over time

What is chemical & physical weathering?

• physical: the breaking of rock into smaller pieces without changing its chemical makeup

• chemical: the breakdown of rock through chemical reactions that change its composition

What is undercutting?

a process of erosion where the base of a slope, riverbank, or cliff is worn away faster than the upper part causing the structure above to become unstable

What are the factors of global climate change?

• composition of atmosphere

• amount of solar radiation

• effect of oribital paramters

• atmospheric/oceanic circulation

• interactions with biogeochemical cycles

• albedo of earth

• catastropic effects

• human impacts

What is a warming loop?

• something that causes warmer conditions

• as a result some snow and ice melts

• this lowers the surface albedo

• lower albedo causes more solar radiation to be absorbed at the surface

• more absorption of solar radiation causes warmer conditions

What is a cooling loop?

• something causes colder conditions

• as a result some more snow and ice forms on the surface

• the raises the surface albedo

• higher albedo causes less solar radiation to be absorbed at the surface

• less absorption of solar radiation causes cooler conditions