Of all of the sciences, geology is the one where deep understanding of the underlying processes eluded us the longest. Even the two other contenders -- genetics and astronomy -- were at least partially unraveled sooner. Plate tectonics, the model that provides a framework for comprehending just about every other geological process, wasn't elucidated until Frederick Vine, Drummond Matthews, and Harry Hess came along in the early 1960s. Until then, geology texts fell back on hand-waving explanations like synclines and anticlines, and pretty much ignored questions like why most of the world's volcanoes and major earthquakes fall along a tracery of curves that encircle the Earth like the stitching on a baseball (the most famous of which is the Pacific Ring of Fire).
Part of the reason it took us so long to figure all this out is because geological processes are, for the most part, slow, so it's easy to look around and conclude that the Earth has pretty much always looked like it does today. Then... they discovered anomalies like marine fossils in the Himalayas, Kansas, the Rockies, and right here in my own neck of the woods in upstate New York. It took the brilliant Scottish geologist Charles Lyell to recognize that if rates of sedimentation are fairly constant, then big sedimentary rock layers like the White Cliffs of Dover must have taken tens of millions, rather than thousands, of years to form. The recognition of how slow most geological phenomena were meant the Earth was a great deal older than the six-thousand-year estimate by Archbishop Ussher -- setting up the first of many clashes between geologists and the church establishment.
But "usually slow" doesn't mean "always slow." Sometimes major geological processes can occur, literally, overnight. Take, for example, the appearance in 1943 of a new volcano, dubbed Parícutin after the nearest town, in a Mexican farmer's cornfield.
The locals did at least have a little bit of warning. For weeks prior to the initial eruption, they had heard sounds "like thunder but with no clouds in the sky," now thought to be the rumblings of magma moving beneath the surface. There were over twenty small earthquakes over 3.2 on the Richter Scale, and hundreds of smaller ones -- the day before the eruption, there were more than three hundred small earthquakes.
What happened next is best said in the words of Dionisio Pulido, the farmer who witnessed it first-hand:
At 4 p.m., I left my wife to set fire to a pile of branches when I noticed that a crack, which was situated on one of the knolls of my farm, had opened... and I saw that it was a kind of fissure that had a depth of only half a meter. I set about to ignite the branches again when I felt a thunder, the trees trembled, and I turned to speak to Paula; and it was then I saw how, in the hole, the ground swelled and raised itself two or two and a half meters high, and a kind of smoke or fine dust – grey, like ashes – began to rise up in a portion of the crack that I had not previously seen... Immediately more smoke began to rise with a hiss or whistle, loud and continuous; and there was a smell of sulfur.
By the next morning, where Pulido's cornfield had been was a scoria cone fifty meters high; a week later, it was double that. It was continuously erupting volcanic bombs and small pyroclastic flows, and Pulido decided that his home and land were done for, so he got the hell out. Before leaving, he put up a sign saying "This volcano is owned and operated by Dionisio Pulido" -- indicating that even in dire circumstances, you can still hang on to your sense of humor.
The entire eruption cycle went on for two years, and by the end, there was a massive conical mountain, over four hundred meters tall, where before there'd only been a flat valley. Only three people died during the eruption, and oddly, none of them were from the lava or pyroclastic surges; the three died when they were struck by lightning during an ash eruption. (The tiny particles of volcanic ash are often electrically charged; lightning strikes in ash columns are common.)
It did, however, render much of the (former) valley uninhabitable. Here's a photograph of the ruins of the old church of San Juan Parangaricutiro, which was destroyed by lava and ash along with the rest of the village of the same name:
At the time of the eruption, all that was known was that it added another peak to the Trans-Mexican Volcanic Belt, which runs east-west across the entire country and includes much more famous volcanoes such as Popocatépetl. Since then, we've learned that the whole range owes its existence to the subduction of the Rivera and Cocos Plates underneath the North American Plate at the Middle America Trench; the waterlogged rock and sediments are pulled down into the upper mantle, heated, and melt, forming the magma that eventually erupts somewhere behind the trench.
But at the time, the appearance of a volcano was a source of mystification both to the locals and the scientists. To be sure, some geological phenomena are sudden; earthquakes, for example, often happen without much in the way of warning (and accurate earthquake prediction is still a dicey affair). But we're used to things pretty much staying in the shapes and positions they were in before. It takes a huge earthquake -- the 9.2-magnitude Anchorage megathrust quake comes to mind -- to radically reshape the land, in this case raising a long stretch of coastline by as much as nine meters. And while big volcanic eruptions, such as the current one from Mount Etna, are spectacular and can be deadly, most of the time they're from volcanoes we already knew about.
Parícutin, though, kind of came out of nowhere, at least by the scientific understanding of the time. And that's one of the benefits of science, isn't it? It allows us to understand the processes involved, not just name them after they've happened. While we're still not at the point where we can predict with much lead time when something like this will happen, at least now we can say with some assurance that we understand why it happened where it did.
Little consolation to Dionisio Pulido, of course. I'm guessing that "owning and operating" a volcano was nowhere near as lucrative as his cornfield had been. But that's life in a geologically active area. However much we understand about the science behind such events, it's good to keep in mind there's always a human cost.
