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Last two lectures after the midterm.

Tsunami causes

Volcanic eruptions
meteor impacts (biggest)
icebergs falling from glaciers (smallest)


When a tsunami comes ashore (wavelength drops, height increases, period stays the same)

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

2004 Indian Ocean Tsunami

-deadliest in human history

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

Cause: Landslides

Large displacement of water causing Tsunami

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)

Sources: Storm Surge

-low pressure in hurricane eye (small)
-high wind speeds (Large!)

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

Sea Level Rise: Local effects (BC)

-mainland is submerging, but Vancouver Island is emerging

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


-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)

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