Geology

Things affecting shorelines

waves (lots of energy in them, move sediment, erosion, deposition)

rivers (sometimes have a lot of sediment moving down them, can deposit into beaches)

delta (sediment deposited from river)

wind (always acting at the shore, moving sediment to and across the shore)

fault (can uplift or lower coast, shapes shoreline)

tide (low tide and high tide)

offshore currents (going horizontal to shore)

changes in sea level (glacial melting, warms up)

factors that change appearance of shoreline

strength of waves (stronger waves may pull out finer material)

slope of seafloor (controls when waves impact shoreline)

orientation of the coast (waves hitting shoreline may erode away edge)

hardness of bedrock

amount and size of sediment

climate (wet, soils, stabilizing vegitation)

uplift or subsidence (where the rising sea level starts to cover land)

what are tides?

when the sea level rises based on something

• high tide (~every 12 hrs 24 min)

• average sea leverl

• low tide (~every 12 hrs 24 min)

what causes tides

rotation of earth changes where excess force of gravity, and water mounds up following the force of gravity

why are some tides higher than others

more than normal

• both the moon and the sun are in alignment, so the force of both the moon and the sun acts as a gravitational pull causing mounding

less than normal

• the moon and the sun are at 90 degrees to each other,

how waves are described

crest is high part, trough is low part, wave base, wave action

propagation of waves

• waves moving in an orbit based on the A, B, and C spots

• moves more towards surface than at wave action (towards seafloor)

wave formation

wind blows across surface

gas molecules collide with water to form waves

waves increase in size

wave collapses if becomes too swteep

breaks where wave base = ½ wavelength

how waves interact with the shoreline

swirl away loose pieces of bedrock or break off new pieces

grind and break clasts, making sand and stones that promote erosion

waves bend (refract) if approach shore at an angle

part that encounters bottom of seafloor slows, bending wave

waves break directly on promontory from several sides

• bays protected from largest waves

how sand and sediment get moved on a beach

sand washed back and forth by waves

• deposited in slump or pile of sand

• water flows downslope carrying sediment off of the beach

• wind blows sand on, off, or along the beach

• sediment moves laterally along coast if wave at angle to beach

what determines whether a shoreline gains or loses sand with time

rivers provide influx of sediment

sedi8ment kalrgely from erosion on land

dunes with sand mostly from beach or river

beach erosion and slumping rocks add sediment to shore

reefs erode, adding material to the system

currents transport sediment along coast

shoreline featurs carved by erosion

sea cliffs - a ton of material removed to not even have a beach

caves and sea arches - the energy is focus more on around the headland than the front of the headland

pinnacles and sea stacks - if erosion of sea arch continues, it could collapse and create this

wave-cut platforms - flat features cut by high tide

formation of a sea cave and sea stack

promontory extends out into the sea, weak or fractured rock forms cave, continued erosion leads to collapsed roof of cave

energy will try to erode and eventually create equilibrium in a straight coastline

shoreline features formed by deposition

sandbar (offshore) - if vegitation is on a sand bar, it is a lot harder to move

spit - connected to land, waves follow along land depositing more sediment, so spit will continue to get longer based on sediment deposition

barrier island - offshore and not collected,

baymouth bar - completely encloses a lagoon

observe formation of spits, baymouth bars, and barrier islands

spit forms when waves and longshore currents transport sediment along beach

spit can grow into baymouth bar with continued deposition

if sea level rises, erosion will split land and spits and bars may become barrier island

hazards along shoreline

waves, storm surge, strong winds

observe damage from hurrican fran in 1996

shoreline gets eroded away in spots, tears down houses from getting ride of ground

approaches to shoreline problems

sea wall (concrete wall) and riprap (big rocks of stone)

beach nourishment

breakwater (features parallel to beach to break up big waves) groins perpendicular to beach break up waves horizontally

jetty (long strip of concrete surrounded by riprap to prevent chipping and harbors

hurricane related changes to a barrier island

massive erosion on one side and deposition on the other

Emergent Coast Features

erosion incises into beach and other land

wave-cut notches and terraces exposed

reefs may become exposed

sandbar can become coastal dunes

characteristics of submergent coasts

chesapeake bay: originally a river valley

fjords: once glacier-carved valleys

characteristics of emergent coasts

wave-cut notch about sea level (from where waves used to erode out land)

coral reefs exposed when sea level drops or land uplifted by tectonics

wave-cut platforms now marine terraces high above sea level

how would each factor affect sea level

glaciers - increase in glaciers = fall in sea level, less glaciers = rise in sea level

spreading rate - slower seafloor spreading = drop in sea level, faster spreading = rise in sea level (broader part of ridge hot & higher)

ocean temperature

ocean cools, water contracts = drop in sea level, warming oceans = rise in sea level

how the position of continents influences global sea level

ice sheets form on land so land must be at high latitudes

abundent glaciers = drop ihn sea level

less glaciers if continents at lower latitudes = keep sea levels high

loading and unloading affect elevation

ice pushes down on land surface; seas inundate region

weight unloaded, region flexes back up (isostatic rebound)

rebounding continues for 1000s years after ice gone

evidence left behind by glaciers

liquid water in high places, landscape looks eroded away

glaciers carve into land and deposit sediment

u-shaped valleys

striations

glacial till

glacial erratic (big blocks of rocks in random spots)

Formation

glacier forms where accumulation of snow and ice exceeds loss,

glacier loses ice and snow by melting, wind erosiong, and sublimation

equilibrium line: losses equal accumulations

glacier moves by slipping along base and internal shearing and flow of ice crystals

upper surface fractures and forms crevasses

irregular, dry interface between bedrock and glacier may lock base of glacier

if interface is wet and smoother, glacier may slide

when a glacier encounters water

much higher friction where glacier is on gravel, but much less friction at the sea

front of the glacier speeds up on the sea, and begins to crevass

floating ice spreads and fractures

large blocks may collapse off the glacier (calving)

landscape features of mountain glaciers

mountain glaciers

snow fields

moraine

terminus

cirque

aretes

hanging valley

landscape features of continental ice sheets

features appearing above ice

asker

kettle lakes

drumlins

glacial outwash (sediment)

recessional moraine

terminal moraine

how changes in earth’s til influence global climate

larger tilt = more seasonal (more extreme seasons)

maximum tilt: warmer summers near poles and less glaciation

increase in sunspot activity (warming)

increase in reflectivity (albedo) from snow or clouds (cooling)

release of greenhouse gases by volcanoes (warming)

volcanic ash and dust reflect solar radiation back into space (cooling)