Midterm 2 Flashcards
Why is it not sufficient to be a good swimmer to survive a tsunami?
Debris and the power of the current would make swimming near impossible
How do subduction zone earthquake cause tsunamis?
the elastic rebound from the overriding plate breaking free of the subducting plate causes an uplift in the seafloor causing a wave of water as water first rises and then falls
What direction does an island above a subducting plate move between earthquakes
The island subsides (sinks) as the overriding plate is drawn down by the locked plate interface
What is the magnitude of subduction zone earthquakes that cause tsunamis?
M9 or larger; normally ruptures 100s of miles of a fault
How are tsunami waves traveling through the deep ocean influenced by seafloor topography?
A subduction tsunami is initiated on the seafloor; thus, it involves the full depth of the ocean
How do tsunami waves differ from large wind-blown waves?
Tsunami waves carry a larger volume of water, have a much larger wavelength, and travel further inland
Can a slip on an underwater strike-slip fault cause a tsunami?
No, as strike-slip faults will not cause a change in the height of the seafloor
What happens to a tsunami wave’s speed and height as it approaches shore?
The wave slows down which reduces wavelength, causing an increase in height
What happens to the distance between tsunami wave crests as they approach the shore?
The distance between the crests become shorter
What does “tsunami” translate to?
Harbor wave; this is because sometimes fishermen would encounter no unusual waves out at sea, then find their harbor destroyed by a huge wave
What happens to a boat in the middle of the ocean when a tsunami wave passes underneath?
A boat would rise less than a meter over a period of 10s of minutes and not be aware that a tsunami passed underneath
When does a wave moving toward the shore typically break?
Tsunami waves break when wave height is about equal to the water depth
Why are inlets (natural harbors) a dangerous place to be when a tsunami hits?
Because the incoming water gets trapped and piles up
Can an earthquake on the San Andreas Fault cause a tsunami?
No, the San Andreas Fault is a strike-slip fault and mostly on land
Can tsunami waves be deadly even miles inland from shore?
Yes
What is the approximate number of people killed by tsunamis in the past 1000 years?
Several hundred thousand
Was the 2011 Japan tsunami an unprecedented event in Japan’s history?
No, Japan has a history of tsunamis going back centuries
What is a Japanese tsunami stone?
Stones along the coast of Japan warning residents to not build below them
How do we know that the northwest coast of the U.S. has experienced large tsunamis?
Buried sand deposits along the coast of the Pacific northwest
How long does it take for a tsunami to reach the coastline?
About 5-10 minutes
Why does the sea level dramatically drop before a tsunami hits?
The oscillating wave brings water from the shoreline into it as the amplitude gains in height
Why is it dangerous to return to the beach after a tsunami wave first arrives?
Tsunamis typically consist of multiple waves that hit the shore over the span of several hours
What is a tsunami seawall?
A concrete barrier built near the shoreline to stop tsunamis from reaching inland
How long does it take for a tsunami wave to cross the Pacific?
Almost 24 hours
Why was there a high death toll in the Indonesian tsunami of 2004?
Lack of education about tsunamis and a system to notify the public if a tsunami is suspected
How does the DART tsunami early warning system work?
The DART system detects water pressure changes on the seafloor
What process causes the largest tsunamis?
Asteroid impact, though an asteroid induced tsunami has never been observed
What process caused the largest tsunami run-up recorded in the past 100 years?
A landslide
How long does it take for a tsunami to travel from the Åkerneset cliffs to Geiranger?
About 10 minutes
What generally causes tsunamis at the Hawaiian Islands?
Underwater landslides on the largest island, the only current volcanically active one
What is most likely to cause a tsunami to hit the U.S. east coast?
Underwater landslides on the flanks of volcanoes like the Canary Islands, which have very steep underwater cliff faces
What was the cause of the tsunami the killed 36,000 people in Indonesia in 1883?
The volcanic eruption of Krakatoa
What are the vulnerabilities of Florida if a 10-km-diameter asteroid hit the Gulf of Mexico?
Everything as the impact would cause megatsunamis over 100m tall
What is the difference between the magma and lava?
Magma is melted rock beneath the surface of the earth, lava is melted rock extruded onto the surface of the earth
Is there an ocean of magma beneath the lithosphere?
No, most of the mantle is below its melting point
What is the temperature of the mantle compared to its melting temperature?
The temperature of the mantle is on a curve, most of which is lower than the melting point of rock
What processes promote the melting of hot rocks?
- An increase in temperature
- A decrease in pressure (depressurized melting)
- An addition of water to the mineralogy (hydration-induced melting)
What is the type of volcanism found far from plate boundaries?
Hot spots
What is the process that causes hot rocks to melt at subduction zones?
Hydration induced melting
What does the ring of fire refer to?
Subduction zone volcanism that occurs where plates are subducted, causing a “Ring of Fire” around the Pacific Ocean
Why are there fewer active volcanoes in the southwest U.S.?
There are no active subduction zones in the southwestern U.S.
What process causes hot rocks to melt at hot spots?
Depressurized melting
Where does the rising plume originate from at hot spots?
The base of the mantle
Where does a hot spot plume melt
The base of the lithosphere
Why do hot spots lead to a line of volcanoes?
When a tectonic plate moves over a hot spot, volcanoes initiate over the hot spot then go extinct as the volcano moves away from it, and a new volcano develops
Where are hot spot tracks found?
All over the world
What process causes hot rocks to melt at mid-ocean ridges?
Depressurised melting
What is viscosity a measure of
Resistance of a fluid to flow
What kind of volcano is produced by low viscosity lava?
Broad, shallow, sloped volcanoes
Is the big island of Hawaii the tallest mountain on Earth?
Yes, Mauna Kea is the tallest mountain on Earth as measured from its base to its top
How does a stratovolcano form?
Alternating layers of pyroclastic flows and high viscosity effusive lava flows
What kind of volcano forms when tephra is thrown out of a volcanic vent?
Cinder cone volcanoes
What is an effusive volcanic eruption?
Magma flowing up to the surface through a vent or crack without building up high pressure
Why does pressure in magma build up as it rises toward the surface?
Magma contains dissolved gas in solution form. As magma moves up to the surface the pressure on it from overlying rocks decreases, this causes dissolved gas to expand to form gas bubbles
What is volcanic ash?
Tiny grains of volcanic glass from magma sprayed into the air by gas pressure
What is the combination of magma viscosity and gas content that leads to effusive eruptions?
Low viscosity, low pressure, and hotter temperatures
What is the most powerful type of explosive eruption?
Plinian eruptions
How many volcano-related deaths have occurred in the past 500 years?
More than 250,000
What volcanic hazard leads to the least number of deaths?
Lava
What volcanic hazard leads to the greatest number of deaths?
Pyroclastic flows
Can volcanic flows be stopped by spraying water on them?
Sometimes
Can volcanic flows be redirected?
Sometimes
What are the characteristics of volcanic ash?
Hard, abrasive, corrosive, electrical conducting, and does not dissolve in water
What are the characteristics of pumice?
More air bubbles than scoria
Less dense; floats on water
Light coloured
Used as scouring agent
What is a pyroclastic flow?
A dense, destructive mass of very hot ash, lava fragments, and gases ejected explosively from a volcano and typically flowing downslope at up to 200 mph
Can pyroclastic flows be redirected?
Sometimes
Why are lahars dangerous?
Lahars are avalanches of ash, soil, rock, and water that can occur several days to months after an eruption. The flows can extend 10s of km and can reach 10m high
What is the time frame for volcanic gases to make lakes very acidic?
Weeks to months
What killed almost 2000 people in Cameroon in 1996?
A carbon dioxide gas cloud that descended from the volcanic lake Nyos
What is a harmonic tremor?
A small, “rhythmic” earthquake that lasts for many minutes that occurs when magma moves underground
Can volcanic eruptions be predicted a few days before they occur?
Sometimes as explosive volcanic eruptions are generally preceded by precursors associated with a build up of pressure;
-Gas release increases
-Rapid ground deformation
-Earthquake frequency increases
-Harmonic tremors
Why is the destruction of Pompeii in 79 AD historically remarkable?
-16,000 people were killed
-An amazing description of the eruption was written by Pliny the Younger
-Pompeii was preserved by 80ft ash and dugout, including bodies
What kind of volcano is Mount Vesuvius?
A stratovolcano formed by a subduction zone along the coast of Italy
What volcanic process created Mount Vesuvius?
Subduction and hydration-induced melting
How was Pompeii preserved for 2000 years?
How was Pompeii preserved for 2000 years?
Of the bodies of Pompeii, what was preserved?
Only the volume and the bones
Who was Pliny the Younger?
A roman lawyer, author, and magistrate. He wrote an account of the eruption of Mount Vesuvius and the destruction of Pompeii
Who was Pliny the Elder?
Pliny the Younger’s uncle, a naturalist and commander of the Roman Navy in the Bay of Naples; died trying to rescue victims of the Vesuvius eruption
Why is Yellowstone considered a hidden supervolcano?
Because there is no recognizable sources
Why do geysers erupt but hot springs do not?
Hot springs are continuously replenished due to straight plumbing. Geysers erupt due to bends in plumbing that require a threshold pressure to be achieved before they erupt
How do we know Yellowstone is a hot spot volcano?
Because it lies at the end of a trail of extinct volcanoes
What is the Volcano Explosivity Index (VEI) rating based on?
The volume of ash and other rock ejected
How do different VEI ratings compare to each other?
The ratings are on a logarithmic scale (VEI 7 is 10 times larger than VEI 6 and 100 times larger than VEI 5)
What percentage of the U.S. was covered by ash from past Yellowstone supereruptions?
At least 50%
How does a caldera form?
A large circular depression that forms when the surface collapses into an emptying magma chamber
How many large eruptions has Yellowstone experienced in the past 2.1 million years?
3
What is the evidence for Yellowstone’s very large eruptions?
Three calderas along with the measured ash fallout and the size of its pyroclastic flows
How do volcanologists monitor Yellowstone?
Using a large seismic network to monitor seismic activity, using GPS to monitor ground deformation, and measuring changes in ground temperature
How do we know the size of the current magma chamber under Yellowstone?
Yellowstone’s seismic network and robust seismicity; seismic imaging is used to infer Yellowstone’s substructure
how do we monitor changes in pressure of a magma chamber?
Uplift of the ground, measured by GPS
How do large explosive volcanic eruptions influence climate?
Explosive eruptions emit large amounts of sulfur dioxide which react with oxygen and water vapor in the atmosphere to create sulfuric acid droplets. These droplets block sunlight causing global cooling
What volcanic eruption influenced Mary Shelley to come up with Frankenstein?
The 1816 eruption of Mount Tambora
Why is the Toba supereruption 74,000 years ago considered an important event?
The Toba supereruption caused 10 years cooling of 4°C, which may have triggered a 1000-year ice age
What are giant flood basalts?
Very large volcanic flows that occur over a geologically short time (10s of thousands of years)
What do giant flood basalts originate from?
Mantle plume heads when they first reach the surface then undergo depressurized melting
How have giant flood basalts caused extinction events?
Large amounts of greenhouse gases led to global warming and acid rain
