The Case of the Incomprehensibly Big Super Volcano

The Yellowstone Super Volcano is every American's favorite geological Apocalypse-in-waiting.* Every 700,000 years, give or take a few hundred thousand, this buries a significant portion of the western US in various astounding superlatives. But this article on the recent 4.8 earthquake at Yellowstone has the biggest (and silliest) superlative I've come across in a while. The article states that,

"Late last year a new study into the enormous super volcano found the underground magma chamber to be 2.5 times larger than previously thought — a cavern spanning some 90km by 30km and capable of holding 300 billion cubic kilometers of molten rock." 

Now, 90*30=2700, and 300 billion over 2700 is 111,111,111.1111, or a bit more than 110 million. So for the volume of the cavern to be 300 billion cubic kilometers, the cavern would have to be 110 million km deep, or roughly 8700 times the diameter of the earth, about 2/3 of the distance to the sun. That is one deep hole. With the utmost respect to the Ragnarokian prowess of the great and powerful Super Volcano, I question whether its magma chamber is roughly one third of the entire Earth. Rather, I suspect that this is another case of innumeracy (or at least i-unitacy) on the part of a reporter. 300 billion cubic kilometers of molten rock is not likely, but 300 billion cubic meters of molten rock is quite plausible. A cubic kilometer is a billion cubic meters, so 300 billion cubic meters is 300 cubic kilometers, which is about how big you would expect a 90*30 km cavern to be. Still figuratively, but not literally, astronomical.

The fact that reporters often don't understand units and don't do the basic arithmetic to check numbers is nothing new, but it has only just occurred to me that there is a systematic bias in this. As when NPR casually mentioned the "240 mile deep water" off Alexandria, or when I heard on the radio that a local bank was receiving a bailout in the hundreds of trillions of dollars, reporters always seem to get the numbers wrong in a way that grossly exaggerates the claim. If the magma cavern was stated to be 300 billion cubic millimeters (equal to 300 cubic meters) instead of 300 billion cubic kilometers, a reporter or editor probably would have found that unsatisfying and therefore caught the mistake. If it was instead 300 Sextillion cubic meters, it would look sexy and nobody would likely question it. But there is probably another bias at work. Once a number is really big, substituting another really big number generally doesn't change the impression much, and if one doesn't understand what the numbers mean, it is therefore equivalent. Incomprehensibly Big = Incomprehensibly Big. So overstating your case by a factor of a billion isn't go to raise nearly as many alarms as understating it and thereby eliminating the hugitude.


*You only think you prefer that tired old tectonic fault.

Idiozia

I love Italy. Friendly people, good food, great art, nice weather, etc. But there is something in Italian governance traditions that make me feel okay about not living there. Prime examples are Berlusconi and this, the conviction of six seismologists and a government functionary for failing to predict an earthquake in L'Aquila that killed 309 people in 2009. More exactly, they issued a report that said that it wasn't possible to predict whether or not their would be a major earthquake that year, but estimated the probability as fairly low. The earthquake came, and they are the scapegoats.

Imagine if you will that an Italian man goes to the doctor, and asks if he is going to have a stroke that year. The doctor gives him an exam, some blood tests and a questionnaire, then uses the best available methods to estimate that this man has only a 10% chance of having a heart attack that year. The man goes for a hike, has a heart attack, dies. Should the doctor go to jail for failing to know for sure that the heart attack is coming? Of course not. We don't put people in jail for failing to know things that no one could possibly know. We don't, but apparently the Italian courts do.

Now imagine the Italian government comes to you next week and wants you to produce an expert report on an unpredictable topic for them. Would you be eager to help?

All quiet on the Hayward Fault

For the five years I have lived in the Bay Area, I have occasionally checked this map to see what recent earthquakes have happened round these parts. This is the least activity in a week I have seen. And there has been almost this little for some weeks now. The cluster of small quakes in the upper left corner is "The Geysers," an area of hydrothermal activity that always has many small quakes. On the San Andreas Fault and the Hayward Fault, the two main faults running through the Bay Area, there is not a single anything. No movement. This makes me very nervous. It makes me think that things have jammed. As long as there are many small earthquakes, my fabulously limited knowledge of seismography suggests that tension is being released. For the last several weeks there has been almost no release of tension on the faults around here. I consider it fairly likely we will have a significant earthquake pretty soon here. That said, I really don't know squat about earthquake prediction.