Recently, the Internet has erupted with tales of increased volcanism and more extreme earthquakes. Depending on the writer’s point of view, this geologic bent towards catastrophe appears as either a certain sign of the Biblical End of the World, or as yet another deadly permutation of climate change. We’ll leave the Biblical debate for others, but can anthropogenic climate change actually cause earthquakes and volcanic eruptions?
In a word, yes–but it’s not anything we need to worry about.
How frequent are disasters?
First of all, contrary to popular claim, there is not an increase in geological activity right now. At least, not a significant increase–any event that occurs randomly through time is going to have some clustering, the same way when you flip a coin many times in a row you’ll get a few consecutive heads or a few consecutive tails here and there. It doesn’t mean anything. Statisticians can calculate what these random clusters should look like and how to tell when something more than random variation (something that’s “statistically significant”) is going on. And right now, with regard to geology, it isn’t.
Or, at least it isn’t with earthquakes. We are in a bit of an earthquake cluster these days (2014 had about double the recent annual average of quakes), but a team of scientists analyzed the data and found nothing that differs from chance. They were hoping for more–they suspect that large earthquakes can trigger each other across the globe and they were looking for evidence to support their claim. They didn’t find it. Tough break. As for volcanism, I found assertions that there is no increase, but no description of any studies on the subject. That could mean that there aren’t any, or it could mean the search engines are being distracted right now by a lot of gorgeous color photographs of disaster. But there are plenty of reasons why we could be hearing about a lot of volcanic eruptions even if nothing unusual is happening:
- There are more people than ever before, so the chance of somebody being nearby (with a video camera!) when a volcano erupts is higher than ever.
- We have better data collection than ever before, so the chance of scientists noticing the most remote eruptions is higher.
- A lot of people evidently expect to see evidence of the end of the world these days, and most of us see what we expect.
- Social media exists, meaning that rumors can fly across the world very fast (OMG!)
All these principles apply to earthquakes as well, so the fact that we are in an earthquake cluster is probably irrelevant to public perception.
Ok, but could climate change influence geology?
One of the drivers of all this geologic attention is the new book, Waking the Giant: How a Changing Climate Triggers Earthquakes, Tsunamis, and Volcanoes, by Bill McGuire. The book itself is evidently fairly measured, though its marketing is histrionic to the point of evoking a Hollywood big-budget disaster movie. But marketing aside, there are links between climate and rock.
The most obvious of these links involves isostatic rebound, or earth movements in response to melting glaciers. Glaciers are very heavy, heavy enough to depress the land they lay upon by many hundreds of feet. There is a particularly dramatic example of this principle on Mt. Desert Island, in Maine, where a short side trail brings the visitor to a shallow cave on the side of a mountain. What created the cave? It turns out the ocean did–even though the actual ocean depth was somewhat less than it is now. When New England was under a glacier, the weight of the ice pressed it down and then the ice melted faster than the land could rise. The sea, swollen from all that glacial meltwater, rushed inland, drowning the coastal plain and even filling the Champlain Valley with sea water–and that high sea, breaking against the resistant granite of Mount Desert Island (at the time, Islands, plural), hollowed out a cave–something like a larger version of today’s Thunder Hole, for those familiar with the area. In time, the land rebounded and lifted that sea cave up hundreds of feet above the water, where it is today.
All that rebounding causes earthquakes. Try leaning your weight on the hood of a car and then letting go suddenly–you’ll hear a noise just as your weight comes off the car, when the temporary dent you made fixes itself. That noise is a vibration, a car-quake, if you will. The earth does exactly the same thing, it just takes a lot longer.
And I mean a lot longer. In fact, New England is still rebounding after ten thousand years ice-free.
And the rebound must also have taken a very long time to get started, because the sea had time to carve out that cave–in granite, an almost unimaginably hard and wear-resistant rock. Under some circumstances, it can literally take and keep a smooth polish for thousands of years. I’ve actually seen it, bedrock surfaces still as smooth as a counter-top, just as the glacier left them. How long did it take the waves to chew away that sea cave before the land lifted up?
So, when Dr. McGuire claims that melting glaciers in Greenland and Alaska could cause earthquakes, he is almost certainly correct–but that doesn’t mean we should get ready for a summer blockbuster come to life. Now, the temperature is rising now much faster than it did at the end of the last ice age, and I wouldn’t rule out the possibility of something horrible getting triggered by that insane speed, but we should really focus on the disaster that is actually happening right now instead of worrying about that.
There are also hints that yes, climate influences plate tectonics (which in turn involves earthquakes) and volcanism. Tsunamis follow from earthquakes and volcanism, so they, too are implicated. But again, the connections between these phenomena and anthropogenic climate change are tenuous and probably won’t make any difference any time soon.
Climate changes of the past definitely have influenced geologic processes, besides the isostatic rebound-related earthquakes I already described. Faster erosion from stronger monsoon rains has lightened the Himalayas enough to give the Indian plate a counterclockwise spin (over millions of years). And massive ice-melt events have been followed by dramatic increases in volcanism, possibly because the loss of ice-weight from the continents, combined with increased water-weight over the ocean basins, changes stress patterns in the Earth’s crust, triggering some volcanoes to erupt. Although speed of change is definitely part of the picture, and we are looking at some incredibly fast changes right now, there is a reason why “geologic” is a synonym for “slow.” At this time, it looks like we can expect a lag of about 2,500 years before volcanoes respond to climate change.
So, where does all this leave us?
I am trained as a scientist, so accuracy is important to me. I find it irritating in the extreme that some writers are evidently making it sound as though something that may happen over the next several thousand years is an imminent catastrophe. Also, I care about general science literacy and I do what I can to further it. But in pointing out that geologic change is very slow I do not mean to say it is unimportant. If what we’re doing now means that our descendents 2,500 years from now have to cope with a lot more earthquakes and volcanic eruptions, then that is enough reason to stop and do something less damaging. After all, consider that 2,500 years ago, Rome became a republic. What humans do matters across long time spans.
Finally, as the cartoon above suggests, we hardly need to invoke earthquakes and volcanoes and tsunamis to argue against changing the climate–we already have flood, fire, and famine to contend with, quite literally.
Isn’t that enough of a reason?