Sea Level lecture 3- Short-term drivers of relative sea- level change Flashcards
Can we think of short term and long term drivers of sea level independently?
No
Discuss coastal forests.
Long term sea level change can inundate the forest and kill the trees
Large earthquakes can cause the land surface to drop and forest dies.
Land level change causes marine water
Name a coastal forest.
Girdwood River, Alaska (1964 earthquake)
Discuss the earthquake deformation cycle in relation to 1964 Alaska earthquake. (Sea Level)
Continual deformation over time of NA and Pacific plate.
Geological and sediment record of the earthquake through soil, marine sediment and salt marsh.
Drop into inter tidal zone
Repeated sequence.
What is coseismic phase?
Earthquake
What happens during interseismic phase (subduction zone)?
Between earthquakes plates slide freely at great depth where hot and ductile.
At shallow depth where cool and brittle they stick together.
Slowly squeezed, the overriding plate thicken.
What happens during coseismic phase (subduction zone)?
During an earthquake leading edge of the overridng playe breaks free springing seaward and upward.
Behind, the plate stretches; its surface falls.
Vertical displacements can set off tsunami.
What happens at each stage of earthquake deformation cycle in relation to RSL?
- Rapid post seismic uplist - RSL fall
- centuries long inter-seismic uplift- RSL fall
- Pre-seismic submergence- RSL rise
- Rapid co-seismic submergence
Have all subduction zones had large earthquakes during written records?
No
E.g. Mw 9 earthquake along Cascadia subduction zone on 26 Jan AD 1700 probably at 9pm.
No observational records but sedimentological records can be used
Are tides predictable?
Yes
Can there be deviations in tides?
Yes (short term)
What can cause short term deviations in tides?
Hurricanes and associated storm surges.
Weather systems
What are storm surges sensitive to?
Changes in storm intensity, forward spped, size, angle of approach to coast, central pressure and shape/characteristics of coastal features.
What is a storm surge?
An abnormal rise of water generated by a storm, over and above the predicted astronomical tides
What is a storm tide?
The water level rise due to the combination of storm surge and the astronomical tide.
How can geomorphology affect storm surges?
Can chape it and increase magnitude.
E.g. if funnelled through an estuary
What happens during a storm surge?
Wind driven piling up of water
Can happen with tropical storms and mid latitude extra tropical storms
When moving inland and strong winds, pushing water ahead of it
Name two hurricane with large storm surge impacts.
Katrina - 2005
Sandy - 2012
Discuss 3 large storm surges in europe.
2013 - December 5-7. 0 deaths.
1953- Jan 31- Feb 1, 2533 deaths. Most severe in Netherlands.
1703- December 7. many casualties. England, Belgium, Netherlands and Germany.
How can ocean currents affect sea level?
Speed of flow controls how much water is held within that
Flow quicker = more water
Flow slower = ledd water as it will billow off to the side
NAO can have an affect
Is Gulf Stream slowing down or speeding up?
May be slowing down
What is sunny day flooding?
Coastal inundation related storms due to storm system but can occur on a sunny day.
What is GIA and nuisance flooding?
High tide is enough to cause some form of flooding, becoming more common
What does GIA stand for?
Glacio-isostatic adjustment
How does groundwater extraction influence sea level?
Makes it easier for tides to inundate areas.
Can pro-glacial forebulges affect sea level?
Yes
Can RSL be influenced by GIA and storm surges?
Yes
