Comprehensive Geosciences in Movies: Tsunamis, Volcanoes, and Catastrophes

Subduction zone earthquakes

The most common means of generating a tsunami is elastic rebound during a large subduction zone earthquake.

Tsunami generation

Anything that can displace a huge volume of water vertically can cause a tsunami.

Wind-blown waves

have short wavelengths, brief periods, and no additional water mass behind the wave front.

Tsunami characteristics

Tsunamis may not be taller than the wind-blown waves, but they have a long wavelength, and a large water mass builds up behind the wave front.

Tsunami in deep water

Tsunamis in _ water are shorter in wave height, longer in wavelength, and faster.

Tsunami in shallow water

Tsunamis in _ water are taller in wave height, shorter in wavelength, and slower.

Water wave breaking

Water waves will typically break when the wave height equals the water depth.

Earthquakes causing tsunamis

Earthquakes along convergent plate boundaries with magnitudes 7.0 or over can cause tsunamis because they displace large amounts of water vertically from subduction zones.

Transform plate boundaries

Transform plate boundaries can't cause tsunamis.

Swimming and tsunamis

Being a good swimmer isn't enough because the amount of debris and the force of the debris and waves can easily injure people in the tsunami's path.

Tsunami stones in Japan

In Japan, dozens of tsunami stones were planted along its coast to warn residents not to build below them; some of these stones are 600 years old.

Sand deposits

Sand deposits indicate past tsunamis along the Washington/Oregon coast.

Tsunami fatalities

Several hundred thousand people have been killed by tsunamis in the past 1000 years.

Seismic shaking near shore

Significant seismic shaking near the shore means you have 20-40 minutes to head to high ground before a tsunami hits.

Sea level drop before tsunami

The wave trough often arrives before the wave crest.

Danger of returning after tsunami

Tsunamis consist of multiple waves, and the 2nd and 3rd are the most powerful because the energy from the previous wave contributes to the 2nd and 3rd.

2004 Indian Ocean tsunami

Many people died around the Indian Ocean due to the 2004 tsunami.

DART tsunami early warning system

Sends tsunami warnings 15 minutes after an earthquake, including the path and size estimates.

Sensors on the seafloor

Measure water pressure, and the measurements are sent by acoustic signal to a buoy.

Buoy

Sends a signal to the satellite, which is then sent to early-warning stations on land.

Asteroid impacts

Have the potential to cause the largest tsunamis.

Submarine or underwater landslides

Can cause displacement in the water, generating tsunamis in Hawaii.

Tsunamis in the Atlantic Ocean

Likely caused by submarine or underwater landslides, with the U.S. East Coast being vulnerable.

Largest tsunami runup in the past 100 years

Recorded because of an avalanche into the Lituya Bay, Alaska 1958.

Tectonic settings for volcanism

Include mid-ocean ridges, subduction zones, and hot spots.

Volcanism at mid-ocean ridges

On average, most volcanism occurs here.

Hot spot volcanoes

Are the only ones that can form away from plate boundaries.

Magma in the mantle

Only occurs at specific locations and under specific conditions; it makes up a small percentage of the mantle volume.

Decompression melting

Occurs when pressure decreases, causing already hot rocks to melt.

Flux melting

Occurs when volatiles like water are added, decreasing melting temperature.

Heat-induced melting

Occurs when temperature increases, causing rocks to melt.

Melting processes at tectonic settings

Mid-ocean ridges & Hot spots: Decompression melting; Subduction zones: Hydration-induced melting.

Hotspot volcanism

Leads to a chain of volcanoes due to the movement of tectonic plates over a plume of hot rocks.

Ring of Fire

Refers to volcanoes that have formed inland of the trenches of the Pacific Ocean at subduction zones.

Viscosity

A measure of the resistance of flow in fluids.

Stratovolcano formation

Formed by alternating layers of pyroclastic flows (explosive) and lava flows (effusive).

Eruption layers in stratovolcanoes

Show how viscosity and dissolved gas content differ per eruption.

Basaltic

Low silica content (mafic), higher temperatures, low viscosity & low gas content → effusive

Andesitic

Intermediate silica content, temperature, viscosity & gas content → in-between effusive and explosive

Rhyolitic

High silica content (felsic), lower temperatures, high viscosity & high gas content → explosive

Dissolved gas behavior

At certain depths, the mantle has dissolved gas as a solution → closer to the surface, pressure decreases and expands into gas bubbles

Gas bubbles

Gas bubbles take up more volume and cause pressure to build up

Hawaiian eruption

Calmest type with fluid flows and low dissolved gas content; lower volume and lower pressure

Strombolian eruption

Driven by bursting large gas bubbles made from a collection of smaller bubbles; lower volume and higher pressure

Vulcanian eruption

Strong enough to generate shockwaves; higher volume and lower pressure

Plinian eruption

The largest and most violent; can shoot up columns of pulverized rock and ash miles into the atmosphere; higher volume and higher pressure

Volcano-related deaths

More than 250,000 people have been killed by volcanic hazards in the past 500 years.

Pyroclastic flows

Heavier parts (volcanic gas, ash, & rocks) from an eruption are pushed down the flank of the volcano at high speeds (200 mph) by expanding hot gas (1000 ℃)

Lahar

Mudflow of an avalanche of rock, ash, soil, and water that can travel for many miles and occur days or months after eruption

Volcanic ash

Shards of broken gas bubbles left over from the magma, smaller than sand grains, hard, abrasive, coercive, electric conducting, and doesn't dissolve in water

Effects of 15 cm of wet ash

Can cause a roof to collapse

Effects of 5 cm of ash

Can kill crops

Effects of 1 mm of ash

Can shut down an airport

Volcanic gases

Sulfur & carbon dioxide that cause the least deaths far from the volcano

Prediction of volcanic eruptions

Can be predicted within days, but aren't straightforward; precursors include increase in earthquake frequency, volcanic or harmonic tremors, release of gas emissions, increase in surface temperature, and rapid ground deformation

Harmonic tremors

Continuous release of seismic energy due to the movement of magma underground, longer duration and density on the seismogram compared to earthquakes

Pompeii destruction in 79 AD

A detailed description of the eruption was written down by Pliny the Younger; 2,000 people were killed and Pompeii was buried under more than 30 ft of ash

Pliny the Younger

Famous for writing an account of the eruption of Mount Vesuvius and the destruction of Pompeii

Volcano Explosivity Index (VEI)

A measure of the explosivity of a volcano, including the height of the eruption column and the volume of ejected materials (ash and rocks)

VEI level differences

As you increase in one VEI, the release is 10 times more volume of ash and rock than the level below it; e.g., VEI 6 = 10 ㎦ → VEI 7 = 100 ㎦

Geysers vs. hot springs

Geysers erupt due to pressure build-up from underground reservoirs, while hot springs flow straight to the surface

Yellowstone hotspot evidence

Because it lies at the end of a trail of extinct volcanoes

Large explosive eruptions at Yellowstone

3 extremely large eruptions, only 2 of which were supereruptions, ranging from 280 to

Helens (1980)

Ash coverage from Yellowstone supereruptions

VEI 8 = Supereruptions; Huckleberry Ridge Tuff and Island Park Caldera: 2500 ㎦ (2 million years ago); Lava Creek Tuff and Yellowstone Caldera: 1000 ㎦ (600,000 years ago)

Magma chamber size measurement

Imaged by measuring the change in speed of seismic waves (earthquakes) as they pass under the park; waves move more slowly through molten rock than through solid rock

Monitoring pressure changes in a magma chamber

Uplift of the ground is related to seismicity; earthquake swarms are caused by the movement and release of carbon dioxide

Global consequences of large explosive volcanic eruptions

Global cooling occurs as eruptions emit large amounts of ash and sulfur dioxide, which react with oxygen and water vapor to create sulfuric acid droplets that block sunlight

Example of global cooling

Mt. Pinatubo eruption caused a global cooling of ~0.5 °C for a year

Giant flood basalts

Lava flows with volumes of 1000s of times those of ordinary eruptions that can lead to mass extinctions due to the release of large amounts of greenhouse gases