coastal landforms on sea level change Flashcards
what can sea level changes result from
-a change in sea level of acutal sea
-downward or upward movement of the land
what determines where there is an overall rise or fall in sea level
-the fastest or most significant movement (change in sea level or movement of land)
whats a positive change
an overall rise in sea level
whats a negative change
an overall fall in sea level
what is marine transgression
-when there is a rise in relative sea level and sea flows over the land
-cover areas which would have been exposed before
what is marine regression
-sea levels fall
-land once inundated by the sea is revealed
what will coasts do during marine regression and transgression
regression- advance
transgrresion- retreat
what are changes in level of the actual sea called
eustatic changes
what are movements associated with the depression or uprising of land called
isostatic movements
what are isostatic movements of land due to
-the addition or reduction of weight
-due to accumulation of sediments, ice or large quantities of lava flows
is a localised impact
what scale effect do eustatic changes have
a global effect due to interconnected nature of worlds oceans basins
what is glacio-eustatic
-changes in sea level due to accumulation and melting of ice that covers continental land
what doesnt influence the sea level
-growth or decline in size and amount of floating sea ice
-because sea will displace equivalent of its own mass of water
what effect does acculumation of ice during glacial advance have
-can depress the earths crust
what does melting of ice during interglacials result in
-isostatic rebound
-land uplifts to restore state of equillibrium
what is hydro-isostatic subsidence
-as ice melts there is a eustatic sea level rise
-results in marine transgression and weight of water can depress the continental shelf
what are steric changes
-how changes in atoms in molecule are arranged
what are examples of steric changes
-as oceans cool they reduce in size
-as oceans warm, they expand in size
-known as thermal contraction and expansion
-decrease in salinity will result in sea level rise
whats an epeirogenic movement
-large scale vertical tectonic motions of crust involving depression or uplift of ocean floors and continents
what are tectono eustatic changes
-linked to epeirogenic movements
-if shape of ocean basin is altered, reduced in size and global rise in sea level
what are orogenic movements
-associated with mountain building epsiodes in places where tectonic plates converge
how do orogenic movements influence the land
-in mountain building regions, displacement in height of land can be gradual or sometimes sudden (eq)
-when displacement leads to uplift of land- lower sea level
-when displacement leads to loweing of land- higher relative sea level
what are sedimento eustatic global changes?
-due to sediment accumulation
-large accumulation of sediments carried from land to offshore locations
effect of sedimento eustatic changes on sea level
-can reduce basins holding capacity
-rising sea level
-sediment mass could depress ocean floor, increasing oceans volume leading to fall in sea level
steps of sea level change due to glacial advance and retreat
-during glacial period, temp fall and ice sheets, caps and glaciers form on land leading to global eustatic fall (negative change)
-continental ice increases in size (localised isostatic depression of land) creating positive change
-temp rise during interglacial, ice melts, global eustatic rise in sea level (positive change)
-continental ice melts as weight of land decreases isostatic uplift takes place (localisd negative change in base level)
when are emergent coastlines created
when there is a relative fall in sea level
when are submergent coastlines created
-when there has been a rise in relative sea level
landforms on emergent coastlines
-raised beach with former beach material or wave cut platform now vegitated
-present storm beach
-fossil sea cave
-old wave cut notch
-cliff seperating raised beach and present beach
when are emergent coastlines evident
-when each deposits and marine shell beds found above present day high tide level
when does a terrace form
-the raised shore platform with beach deposits creates terrace
-indicated sea must have been at a relatively fixed level for a long time to have allowed platform to develop
what causes the relict cliffs to not be as steep
-break down via sub-aerial processes
what happens to depositional features in emerging coastlines
-salt marshes increase their extent
-beaches and dunes may widen as sediments washes ashore
landforms on submergent coastlines
-rias and fjords
what does positive change in sea level mean
-overall shape of coastline will be changed
what happens when sea levels rise (either eustatic rise or tectonic subsidence)
-some features origionally formed at sea level wjem seas where lower than present completely submerged
where are rias more common
-along discordant coastlines
how do rias form
-when global sea levels lower than present, base level lowered, rivers have potential energy to cut downwards
-rivers erode deep river valleys
-when sea levels rise, deepended segments of river filled as sea level increase
what are the characteristics of rias
-dendritic draining pattern
what are fjords
-drowned glacial valleys shaped by action of ice and been submerged
where are fjords best formed
-at higher altitudes where effects of ice are more profound
features of fjords
-steep sides
-flat bottoms
-U shaped valley
-straight sided and more narrow than rias
-submerged lip at seaward end-marks former extent of glacier
what happens to depositional landforms due to emergence
-salt marshes widened may shrink
what are fiards
-sumbmurged lowland areas that have been glaciated in past
-much wider and shallow and less branhed than fjords
what is glacioeustacy
-oscillation in sea level due to advance or retreat in ice
what is glacioisostacy
oscillation in land level due to advance or retreat in ice
what is the process of sea level change called
eustacy
what is the process of land level change called
isostacy
what is the name for when land returns to normal/ equillibrium
isostatic rebound
what do the features of a submergent coastline depend on
-if the drowned coastline was previously an upland or lowland area
what does the effect of an upland area have on submergent coastlines
-when drowned, water off coast tends to be quite deep
-wave action is strong so more erosion landforms like cliffs and headlands
what is the effect of submerging a lowland area
-when drowned, water tends to be quite shallow
-at low tide, extensive areas of sand and mud exposed
-encourages deposition like salt marshes and dunes
on an emergent coastline, what is a raised beach?
-a clear ledge in the bay
on an emergent coastline, what is a relic cliff?
-sharp rise in the level of land that marks the position of the cliffs that were once on the coast
