Tsunamis Flashcards
Major events that could cause tsunamis
Off shore earthquakes
Volcanic eruptions - pyroclastic flow, caldera and crater collapse
Landslides, lahars that slide into water
Submarine avalanches from big canyons
Tectonic plate movement - Subduction dragging overriding plate so snaps back
What is a tsunami?
A series of ocean waves that send surges of water onto land. The walls of water can reach over 30 m and cause widespread destruction
Why is nz at risk of tsunamis
Tectonic and volcanic activity which causes earthquakes
A long coastline
Landslide or underwater avalanches
Surrounded by continental shelf that has deep canyons
How does a tsunami wave form?
When water is suddenly displaced. Tops of waves move faster than bottoms which cause them to become higher
Characteristics of tsunamis
- Travel much further inland than normal waves
- Have a first wave that is often not the biggest
- Are like very strong and fast moving tides rather than giant breaking waves 4. Result in strong surges and rapid changes in sea level
- Cause much damage+deaths as a result of their strong currents and floating debris
- Move very quickly across the sea at up to 800 km an hour - as fast as a jet plane
- Can cross the whole Pacific Ocean in less than a day
- Lose very little energy along the way because of their long wavelengths
How does an offshore-fault movement cause a tsunami and eg.
Raises or drops ocean floor eg. 2004 Boxing Day tsunami
How does an onshore earthquake cause a tsunami
Movement of a fault near the coast might destabilise sediment in canyons or cause a landslide that might run into water
How does an offshore earthquake - tectonic thrust cause a tsunami and eg.
Overriding plate partially dragged down by a subducting plate might suddenly snap back causing an earthquake eg. 2011 japan tsunami
How does an underwater volcanic eruption cause a tsunami and eg.
Ash cloud and/or pyro clastic flows displacing water also caldera collapse would cause the rebound of massive amounts of water eg. Kermadec volcanoes
How does a caldera or crater collapse cause a tsunami and eg.
Volcanic material slides into the sea or water flows into the new crater and then rebounds eg. White Island, kermadec volcanoes
How does a phreatomagmatic eruption cause a tsunami
Hot magma comes up under water causing the water to flash to steam and move quickly out from the contact area
How does a submarine avalanche cause a tsunami
Collapse of sediment from the slopes of underwater canyons; might be caused by an onshore or offshore earthquake or just gravity if a large amount of sediment accumulates
How does a landslide cause a tsunami and eg.
Anywhere where a landslide can flow into a body of water eg. Ocean, lake, fiord, sound eg. Charles sound landslide during 2003 fiord land earthquake
Two canyons in New Zealand
Kaikoura canyon and cook strait canyon
Cook strait canyon
Most extensive canyon system in nz, walls of canyon become coated with sediment supplied by tides of the cool strait. Layers pile up until gravity or earthquake causes them to fall off the wall
Kaikoura canyon
Deepest canyons in nz. Sediment swept north from otago and Canterbury is trapped, earthquakes cause massive underwater avalanches causing it to collapse
The role of the geosphere in tsunamis and eg.
Earthquake, volcanic eruption, landslide or underwater avalanche initial cause of a tsunami eg. Charles sound tsunami was earthquake that caused landslide
The role of the hydrosphere in tsunamis and eg.
Tsunamis are a feature of the hydrosphere because it involves the movement of water eg. High rainfall in Charles sound may have made the die of the fiord more prone to slipping
The role of the biosphere in tsunamis and eg.
Plants and animals can destabilise slopes, becoming more susceptible to slipping and landslide eg. The steep and rocky slope of Charles sound meant plants were not able to anchor the land so it slid more easily
What causes a tsunami
Major geological event happens under sea, ocean or lake and displaces large volumes of water
Historical tsunamis
Wairarapa 1855 earthquake generated several types of tsunamis
- Movement along wairarapa fault tilted Wellington region causing harbour to flood
- Tsunami waves then surged into harbour
- Earthquake caused part of Cook strait sea floor to rise producing a tsunami
How accumulation of sediment on kaikoura or cook strait canyon cause a tsunami
Sediment eroded from the land is washed out to sea by rivers and carried great distances by ocean currents. Sediment accumulates on steep side of canyon. When sediment has accumulated enough, the sides of canyon become unstable. Strong earthquakes or gravity can cause the sides to crumple and slip. The load collapses causing an underwater avalanche. The water above is pulled down (displaced) and when the sea rebounds a tsunami forms
