Both earthquakes and volcanoes result from ruptures in the Earth's crust, and both can cause widespread human and ecological devastation. But picking a winner in a destruction derby could be a tough call.
Despite Sunday's big 6.0 temblor in Napa Valley, Calif., a 6.9 quake in southern Peru, and rumblings on an Icelandic volcano, these geologic events aren't trying to outdo one another, according to Steve Sparks, professor of earth sciences at the Bristol University (UK).
"There are connections, but it's a very loose connection," Sparks said. "The places where you tend to get lots of earthquakes, you also get lots of volcanoes. Those are the boundaries of tectonic plates."
Napa Valley (and much of California) sits near the boundary of the North American and Pacific plates, which rub against each other about two inches a year. Over time, deformations or strains build up, and the pressure is too much -- the plates slip. Then comes the earthquake.
Peru and Chile are also along a tectonic border zone, while Iceland straddles the boundary between the North American and Eurasian plates, which are slowly moving apart. Iceland has 30 active volcanoes, 13 of which have erupted since it was settled by European seafarers in the 800s. Many sit underneath a massive glacier called Vatnajokull.
In fact, as Vatnajokull and other glaciers retreat due to climate change, many scientists believe we may be entering a time of greater seismic and volcanic activity. Imagine the 1,300-foot glacier acting as crushing deep-freeze for hot lava coming from the Earth's core. Less ice, more magma. "If we have global warming and the ice does melt away," Sparks said, "there may be a small effect."
Luckily, the volcanoes lying below ice sheets in Iceland, neighboring Greenland, and Alaska -- regions experiencing melting glaciers -- are nowhere near as big as those that have exploded in recent times, such as Indonesia's Tamboura in April 1815. That powerful blast released an ash cloud that covered much of the planet, led to summertime frosts, crop failures, and famines, and forced migrations of North American farmers.
Today, it seems like there are more volcanic eruptions and earthquakes because detection and reporting techniques are so much better. Sensitive seismic detectors tell us about remote tremors half a world away, even if there's little or no damage, said Erik Klemetti, professor of geology at Denison University in Ohio.
Scientists are getting better at judging the odds of future earthquakes along certain fault zones by determining the stresses and how long it has been since they were released.
"You can make forecasts which are likelihoods, but what you can't do is say there will be an earthquake next Saturday in Peru," Klemetti said. "That's just not possible. Some argue it will never be possible. The science isn't up to predicting earthquakes."
Some researchers in Japan and California are testing new kinds of early-warning systems that can give residents a few seconds' head start. They detect so-called p-waves, or primary waves that cause little harm. These are quickly followed by secondary waves, or s-waves that are more powerful.
If forced to live next to an earthquake zone or a volcano, Klemetti said he'd choose the quake.
"Its easier to build earthquake-resistant buildings," he said.
As for the earthquake v. volcano destruction meter, even though earthquakes have killed tens of thousands of people in recent history, Klemetti votes for a volcano, hands down.
"In terms of destruction, the big volcano is going to win," he said. "The ash cloud is going to cover a third of the continent. A really big earthquake will be felt in a lot of places but the destructive force will diminish rapidly."