Geological Oceanography: factors affecting coastlines

major ocean basins

• Atlantic

• Pacific

• Indina

• Southern/South Polar Sea

• Arctic/North Polar Sea

active margin

• oceanic plate subducted beneath continental plate

• subduction zones lead to volcanic mountains along coast + earthquakes

active margins coastal features

• rocky/cliff coastline

• few/no beaches (some sand, but most subducted)

• deep water just offshore due to trenches caused by subduction of oceanic plate

bathymetry

shape of ocean bottom

passive margin

• continental shelf + divergent plates

• dominated by sediment buildup from continental weathering

• no active tectonic movements nearby

passive margin coastal features

• sandy beaches

• barrier islands (may protect salt marshes + estuaries)

• broad continental shelf w/gradual increase in sea level buried in sediment from continental weathering

divergent plates

• 2 plates moving apart, seafloor spreading

• causes mid-ocean ridges + hydrothermal vents

rift zone

where seafloor spreading occurs

mid-ocean ridges

• volcanic/seismic activity

• fault zone

• mid-Atlantic ridge, Iceland

fjords

• glacially carved estuaries

• usually U-shaped + deep

moraines

• pile of stuff left over from wherever a glacier stopped growing

• deposit of soil, etc produced as glacier plows across continent

• ex: Cape Cod

rocky coastlines N of Cape Cod

• glaciers scraping away erosion products (beaches)

• → fewer sandy + more cobble/rocky coastlines

• despite being a part of passive margin, bc less time since glaciation for erosions to wear mountains to sand

intact beaches S of Cape Cod

• erosion products from weathering of Appalachians

• + no glaciers to scrape away this material

spit formation

• strong winds → longshore drift

• → mass transport of sediment until mainland ends

• → extension of mainland out into ocean

• estuary/salt marsh may form behind it

barrier island formation

• waves repeatedly deposit sediment parallel to shoreline

• wind + waves shift, continually moving, eroding, growing

eustatic sea level rise

sea level changes due to alteration in volume of water in oceans/change in shape of ocean basin → changes how much water the sea can hold

eustatic sea level rise: glaciers affecting volume of water in ocean

• more/larger glaciers/polar ice caps = lower sea level since water bound in ice

• fewer/smaller glaciers = higher sea level

eustatic sea level rise: displacement of water in ocean basin by geo factors

• due to tectonic/continental drift effects creating mountains/divergent plate boundaries

• due to sediment buildup from erosion products from land

steric sea level change

• results from expansion of water molecules as temp rises

• 50% of sea level rise, more than glaciers

• places that warm faster than others have more of it

isostatic sea level change

• result of increase/decrease in height of land: height of land increases, sea level falls, vice versa

• “apparent sea level change”

• region-specific, doesn’t occur everywhere

isostatic sea level change: subsidence

continent depressed into molten rock below by glacial weight → apparently higher sea level

isostatic sea level change: rebound

when glacier melts/recedes, continent comes back up + apparent sea level lower

glacial forebulge

• when continent depressed, land beyond glacier pushed up

• experiences subsidence as glaciers melt + land comes back up

sediment transport

• sediment transported from streams

• → deposited on continental shelf

• → sedimentary wedge along oceanic + continental plates

• → barrier islands → estuary formation

effects of waves on headlands vs embayments

wave energy converged on headlands due to effects of curved coastline on a straight line of approaching waves

headlands (convex)

• higher wave action →

• → sediment stripped away

• → leaves rocky cliff faces

embayments (concave)

• lower wave action, slower water movement (lower wave energy)

• → sedimentation of materials stripped away from headlands

• → can develop beaches