[EPS80] Midterm 1 Review

Approximately how thick is the Earth’s crust?

7-100 km

Which layers of the Earth are a liquid?

the outer core

What is the definition of an isotope?

atoms with the same number of protons but different numbers of neutrons

What type of radioactive decay changes the mass of the atom by 4 (2 protons and 2 neutrons)?

alpha decay - emits a helium atom

Approximately how old is the universe? (e.g., how long ago did the Big Bang happen?)

13.7 billion years

How were most of the elements heavier than hydrogen and helium in our universe formed?

by nucleosynthesis in previous generation stars

Why do nuclei have to get really close before they can fuse?

They need to overcome the Coulomb barrier - nuclei far apart repel each other; as they get closer, the strong interaction takes over and the nuclei begin to attract each other.

How old is the Earth?

4.5 Ga

What is the difference between fusion and fission?

fusion is when 2 atoms merge and energy is released; fission is when an atom splits apart and energy is released

Co-60 has a half life of 5.27 years. Initially, we have 10 g of Co-60. How much remains after 21.08 years?

0.625 g

Why do gaps in the wavelength of starlight at Tc provide evidence for nucleosynthesis in stars?

Tc has a short half life. None of the isotopes have a half live longer than 4.2 million years. If Tc is still in stars, 14 billion years into the universe, it must be being produced. It cant remain from the Big Bang.

Why is it challenging to make elements heavier than Fe by fusion?

Fe has the highest binding energy per nucleon. Fusion to Fe releases energy; fusion past Fe consumes energy. Have to make it by s/r instead.

Approximately when did flowering plants evolve?

130 Ma

What is the strongest evidence we have for Earth’s oceans becoming oxygen rich?

banded iron formations (BIFs)

When did eukaryotes (organisms with cells comprised of different parts like a nucleus, mitochondria, etc.) evolve?

2.1-2.7 Ga

When did the first vertebrate-like creature (Tiktaalik) come onto land?

375 Ma

When did the dinosaurs go extinct?

66 Ma (K-Pg mass extinction)

Why has the length of a day on Earth changed over time?

tidal friction has slowed Earth’s rotation rate down

evidence for plate tectonics on Earth

glacial striations radiating out from Antarctica; fossil remains that span multiple continents; the fit of the African and South American coastlines

volcanoes or volcanic regions formed by hotspot volcanism

Iceland; Kilauea Volcano, Hawai’i

What happens at a continental-oceanic collision boundary?

denser oceanic crust subducts under less dense continental crust; produces volcanoes, big earthquakes, and tsunamis

What happens at a continental-continental collision boundary?

two continents collide and neither plate can successfully subduct, forming large mountain ranges like the Himalayas

Give an example of a place on Earth where a new ocean may be forming.

East Africa

What happens at a divergent plate boundary?

two plates pull apart; new oceanic crust is made in the middle

What is an example of where a new ocean started to form but eventually failed?

the midcontinental rift, near Lake Superior

What is the distribution of hot spots around the world?

many hot spots are clustered in the Pacific and Atlantic; thought to arise from large low shear velocity zones

What type of plate boundary forms the largest earthquakes (>M9)?

oceanic-continental convergent boundary

factors that contribute to an earthquake’s magnitude (e.g., energy released in an earthquake)

area of fault that slips; amount of slip (in meters); strength of rock along the fault

What are the first types of seismic waves to arrive at a seismic station after an earthquake?

P-waves (compressional waves)

How do we determine the location of an earthquake?

by measuring the time lag between the arrival of P-waves and S-waves at various seismometers (like thunder and lightning in a storm)

Why don’t we use the Richter scale anymore?

The Richter scale uses wave amplitude, but seismometers only record certain frequencies so it was doing a bad job at really large earthquakes.

How much more energy does a magnitude 7 earthquake release compared to magnitude 5?

32 x 32 = 1024x more energy

What affects the intensity of an earthquake?

the magnitude of the earthquake; the distance you are from the earthquake; what materials are between us and the earthquake; the depth of the earthquake

For the same magnitude earthquake, why do people feel earthquakes at a greater distance on the East Coast (e.g., central Virginia) versus in the Bay Area?

The East Coast is made of craton, which rings like a bell when an earthquake happens. Whereas all the faults in the Bay Area dissipate the energy faster.

Where is the Moho (Mohorovicic) discontinuity?

between the crust and the mantle

What is a soft story building?

buildings with unequal levels of resistance on different floors, often with a parking garage underneath

When was the last major earthquake on the Hayward Fault?

1868 (M7)

How long might East Bay residents lose access to water in the event of a Hayward Fault earthquake?

6 weeks to 6 months

What is the point of getting 10 seconds warning through an earthquake early warning system?

time to: shut off gas; drop operating instruments; hold elevators at a floor; put down hazardous chemicals; drop, cover, and hold on

To preserve communications after a really big earthquake, what should you do?

change voicemail to provide updates on your status; text but don’t call, since voice calls use more of the network

What is the difference between magma and lava?

lava = on the surface, magma = in the subsurface (underground)

How do we get the solid mantle to melt and produce magma to feed volcanoes?

reduce the position of the solidus by adding water (e.g., subduction zones); increase temperature of the mantle (e.g., at hotspots); decrease pressure (depth) of a parcel of mantle by making it rise (e.g., oceanic-oceanic divergent boundaries)

Why does the mantle melt at mid-ocean ridges?

plates pull apart, mantle rises up, decompresses without losing much heat, crosses the solidus

Why does the mantle melt beneath Hawai’i?

mantle plume is rising (decompresses) and anomalously hot (heat surrounding mantle) → double whammy to get melting

Where does the water needed to melt the mantle in subduction zones come from?

water being released from the altered oceanic plate being subducted

What general compositional progression do magmas follow as they fractionally crystallize?

basalt → andesite → dacite → rhyolite

What happens to the silica (SiO₂) content of a mgma if it incorporates and melts continental crust?

SiO2 goes up, as the continental crust is Si-rich

What are the most abundant volatiles in magmatic systems?

H2O, CO2, S

major factors affecting the viscosity of magma

water content; melt composition; temperature

Which property affects viscosity more?

melt composition

What are the main volcanic hazards at Mt. Rainier, Washington?

lahars; pyroclastic flows

What are the main volcanic hazards at Kilauea Volcano, Hawai’i?

lava flow inundation; toxic gases

Why is rhyolitic lava more viscous than basaltic lava?

rhyolite has more SiO2

Oh no! An evil wizard is forcing you to stand near a volcanic eruption but, because they are a generous evil wizard, they are allowing you to choose the location of your own demise. Thankfully, you're taking EPS 80 and therefore know a little bit about volcanoes. Which of the following options would be least hazardous to you and possibly allow you to escape intact?

1 km away from a 20 m tall fire fountain

What is the geothermal gradient?

the rate of change of temperature with depth in the Earth

In what setting do pillow basalts form?

underwater volcanoes, typically near mid-ocean ridges

Magmas with a high volatile content lead to effusive eruptions (T/F).

false

The crystallization of iron and titanium oxides will concentrate silica in the remaining magma (T/F).

true

Why does water reduce magma viscosity?

water breaks apart chains of silica tetrahedra

How fast do tsunamis travel?

500 mph

How do tsunamis differ from normal ocean waves?

tsunami waves are much deeper (e.g., whole ocean depth), not just the upper few meters of the oceans

What is the run-up height of a wave?

the maximum height above sea level that the wave reaches after breaking

How can we displace large enough volumes of water to form a tsunami?

meteorite impact into the ocean; landslides (underwater or into a body of water); megathrust earthquake; volcanic eruptions

Approximately how many people died in the 2004 Boxing Day Tsunami in Indonesia?

200,000 to 300,000

How do we know know the atmospheric shockwave from the Tonga volcanic eruption triggered the tsunami (not direct displacement of the water column as is normal)?

the tsunami arrived too early, as the shockwave travels faster than water waves; ocean basins not connected to the Pacific (e.g., Caribbean) had a small tsunami

If you are on a beach, how might you know a tsunami is coming and you should seek high ground?

feel an earthquake; sea starts to retreat like the tide is going out; sea level starts rising quickly; you get an emergency text on your phone; you hear a tsunami siren

If a community is on the coast, and has no high ground around, what can be done to prevent mass death in a tsunami?

vertical evacuation towers

How can we gain early warning for a tsunami?

monitor when earthquakes occur; DART buoys

Can you safely head back to the shoreline after the big tsunami wave has passed to get your stuff/find your family?

no

What evidence do we have for a very large tsunami on the Pacific Northwest in 1700 AD?

reports of a tsunami in Japan that had no local earthquake; indigenous reports; tree rings showing sudden death at 1700 AD

Which tsunami event has the tallest wave height we have evidence for?

Lituya Bay Tsunami (rockfall triggered by an earthquake)