Sunday, February 8, 2015

Quiz on Volcanoes and Earthquakes

Here's a quiz (for fun!) on the natural disasters associated with plate tectonics.

How are you on this topic? Know your earthquakes and volcanoes? (Answers in second half of article.)

From Wikipedia Commons

1. One earthquake can trigger another earthquake:
A) Anywhere in the world
B) Anywhere along the Ring of Fire
C) Only on the same local fault system
D) Never

2. Which are easiest to predict?
A) Earthquakes
B) Volcanoes
C) Tsunamis

3. We are very close to being able to predict earthquakes.
A) True
B) False

4) Earthquakes can only occur at plate boundaries.
A) True
B) False

5) We know where all the earthquake faults are on Earth.
A) True
B) False

6) The largest earthquake (by Richter or moment magnitude scale) recorded in the past 100 years in the USA was in:
A) California
B) Missouri
C) Hawai`i
D) Alaska

7) The deadliest earthquake in the USA in the past 100 years was:
A) The 1964 Alaska Quake
B) The 1906 San Francisco Quake
C) The 2004 Northridge Quake
D) None of the above

8) The biggest volcanic eruption worldwide in the past 50 years was in:
A) The USA's Pacific Northwest
B) Iceland
C) Indonesia
D) None of those

9) It'd be safer to stand next to:
A) A hot-spot volcanic eruption like Hawai`i's
B) A subduction-zone volcanic eruption like Japan's

10) Many scientists think volcanoes, not asteroid impacts, are the cause of at least some mass extinctions.
A) True
B) False

11) There are more earthquakes and erupting volcanoes lately.
A) True
B) False

The answers, as I understand them:

1-C. While some scientists suggest a more remote trigger is possible, no one has made the physics calculations work out, so I'm sticking with the majority who say "it's very, very doubtful distant triggers happen." A quake in Honshu Japan, for instance, could trigger one in Tokyo as the stresses of the fault system are altered. But it won't trigger one in British Columbia or Greece.

2-C. Tsunamis are by far the easiest to predict. Something proximate (earthquake, landslide, asteroid plunging into the ocean) causes them, and usually that trigger is easily detectable. In the shorter term, "drawback," or the receding of the sea from the coastline, can alert an observer to an imminent tsunami. Volcanoes are the next easiest to predict, and scientists are making continual progress there. Earthquakes are nearly impossible to predict at any timescale that would be useful for humans. "There's going to be a terribly big quake just west of Seattle one day soon" is a promise you can take to the bank. But what day? Oh, somewhere between tomorrow and the year 2500. In other words, geological "soon" is not human "soon."

3-B. False. We are nowhere near being able to predict earthquakes. It may be impossible to ever do so in any meaningful way.

4-B. False. Quakes can occur almost anywhere. Intraplate quakes are less common, but they can be powerful and devastating.

5-B. False. We do not know every one--though we probably know of all of the big, active ones. New ones are discovered all the time, sometimes only when there is a sizable earthquake that reveals it.

6-D. Alaska has had the largest nine earthquakes of the past 100 years in the U.S. (And the largest volcanic eruption of the past 103 years.)

7-D. The 1946 Alaska quake caused more deaths than the 1964 one, according to the USGS. What about 1906? That was more than 100 years ago--gotcha with a trick question!

8-D. The 1991 Mt. Pinatubo eruption in the Philippines was the largest, with about 10,000,000,000 tons of magma (rock and ash) ejected.

9-A. While I wouldn't advise being in any eruption, Hawai'i's volcanoes are usually much kinder. The lava moves slowly and is, most days, easy to outrun, even for a little old lady with a cane. This is not true of every hot-spot volcano or every hot-spot eruption. Still, every moderate-sized Pinatubo/Mt. St. Helens/Krakatoa/Mt. Ontake eruption is one you'd best be many kilometers away from.

10-A. True. More mass extinctions are due to vast volcanic eruptions ("traps"), it is generally agreed, than to impacts. In fact, there is still reasonable debate about what killed the dinosaurs--the one impact, or a combination of impact and the Deccan lava flows. Plenty of evidence is piling up for the latter explanation. (Though it's not quite as Hollywood somehow, and the Chicxulub story will be hard to supplant in the public's mind.)

11-B. False. Over the course of the planet's history, there have been and will be steadily fewer as the planet's interior continues to slowly cool. Of course, that's happening on a geological time scale. Over your lifetime, there will be about as many the year you die as the year you were born. What has changed over my lifetime is news reporting. There are more cameras, more sensors, more news outlets, the internet, and so plate tectonic-driven disasters are known about worldwide in an instant. If, rather than relying on the selective perceptions that TV news gives us, we check (I do) the worldwide map of earthquakes over 4.0 every single day, it will become obvious that there are light weeks and heavy weeks but that there is no recent increase. 

Sources: USGS, Wikipedia, and many more.

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