Last two lectures after the midterm.
Tsunami causes
Earthquakes
Volcanic eruptions
meteor impacts (biggest)
landslides
icebergs falling from glaciers (smallest)
Tsunami vs Wind Driven Wave
Wind: relatively short wavelength/period, breakers arrive & recede quickly
Tsunami: ultralong wavelength/period, huge mass of water comes onshore for several minutes
Tsunami waves
-first wave may not be biggest
-trough may arrive first
-indicator- receding sea level (draw down)
Cause: Earthquake
-tectonic plate moving over/under another
-vertical motion
-possible if sea floor is ruptured
Point of Cause: Subduction Zones
-Ring of Fire
-Earthquakes create vertical motion
-Explosive-character volcanoes exist
Cause: Volcanoes
-eruption on land creates landslide into water or earthquake
-underwater eruption causes volcano top to move, gas and lava ejected
Predicting arrival time
-possible because arrival time is based on speed, which depends on water-depth because tsunami are shallow-water waves
DART Buoy System
Deep Ocean Assessment & Reporting of Tsunami
-measures pressure changes caused by open-ocean tsunami
-verifies tsunami existence
-communicates info to warning centres
Storm Surge
-not a wave, but a local change in sea level (10m+)
-can last a few hours- days
-amplifies damage from hurricane-driven waves
-highest to the right of the eye of hurricane (Northern Hemisphere)
Eustatic/Global Sea Level Rise
-Formation & melting of ice sheets on land (since last ice age, sea level has risen 120m, if all ice melted it would rise another 60-70m)
-Thermal expansion (increased volume due to increased ocean water temp, largest contributor to global sea level rise today!)
*we may be underpredicting sea level change!
Local/Regional Sea Level Change
-Isostatic rebound (rise/fall of land due to glacier melt [continues today])
-Tectonic movements (Atlantic Coast subsiding, Pacific emerging)
Sea Level Rise: Effects
-shorelines move horizontally at about 1000x rate of sea level rise for low slope shores (ex Florida)
Therefore, sea level +15cm -> shoreline decreased 150m inwards!
Sea Level Rise: May cause...
-submergence of low-lying areas
-increased erosion
-increased coastal flooding
-inundation of natural ecosystems
Archimedes' Principle
Floating Sea Ice: any object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object
Permafrost
-soil frozen throughout the year underlying most of Arctic
-reinforces soil, limits erosion
-disappearing-> erosion rates increase->threatens coastal areas
Melting Ice Risks: Ex. Barrow, Alaska
-protected from storms/waves by: sea ice (absorbs waves, reduces fetch), bluffs (w/ permafrost), and lagoons
-without ice: waves crash in, storm surge, lagoons flood, bluffs erode
Erosion: Ex. New Orleans
-built on Mississippi delta
-sediment builds up in delta-fans out as new, low-elevation land
-causes location of river to change over time, resulting in marshy, loose land (natural buffer against waves/storm surge)
-city works against this change to lock river in place (and further development)
-creates new problems: lack of new material, no river flow to wetlands
-causes New Orleans to sink!
-natural wetland buffer is easily overwhelmed! (with no material, 30+ miles lost in Katrina can't be replaced)