As an undergraduate, I often selected my courses for the next semester somewhat arbitrarily from the course catalog based on the distributive requirements they filled and, most importantly, on their snazzy titles and two-sentence decsriptions. One of the beauties of attending a liberal arts school is that you can take random classes such as “Phallic Symbols in Ancient Greece” or “Hidden Meanings in the Lyrics of Bob Dylan,” and it’s okay. After all, the point of a liberal arts education is to broaden your horizons, not prepare you for a job in the real world.
So, I chose at least three of my college courses based on their titles alone, “Dinosaurs,” “Volcanology,” and “Introduction to the Earth’s Cold Regions.” While these courses provided me with very little information relevent for my daily life, they did at least prepare me to read this great science news article on the well-preserved remains of a baby plesiosaur:
Note that this extraordinary fossil was found in a layer of volcanic ash, a point that I think is worth emphasizing. Geology texts generally teach that fossils can only be preserved in cooler, slower-moving sedimentary deposits. However, this isn’t true: igneous or volcanic fossils are common, and they often represent the best-preserved biological or archaeological specimens available.
Fossils formed in volcanic ash deposits have the advantage of essentially preserving a snapshot of time. For instance, there are the fossil remains at Pompeii or Tambora, the so-called Pompeii of the East. Archaeologists can’t beat cities preserved in situ in volcanic ash for investigating daily life (and, I suppose, a moment of panic as people realized they were about to buried…) in an ancient city. I also think that there may be something about silica-rich volcanic ash which chemically aids the fossilization process. Certain types of fossils, such as fossilized bones and petrified trees, are formed when silica replaces organic material. Maybe high-silica ash flows are particularly good at preserving fossils– better than mud and sediment, maybe? I don’t think much research has been done on this topic, but it’s a point worth investigating.
Okay, so it’s clear that there are some neat fossils in relatively cool volcanic ash flows. What about lava flows, though? Forming fossils in very hot (900 degrees C or hotter) lava flows seems unlikely. However, there are even rare cases of this. For instance, molds of tree trunks are sometimes found in lava flows because the water excreted by the trees cools the lava enough so that the a mold of the tree can form before the tree becomes toast from the heat of the lava. In Washington state there is also the famous Blue Lake Rhino. The lava flows formed a mold around a dead, bloated rhino. Again, here water played a key role. The water released by this swollen rhino allowed the lava to cool and form the mold before destroying the rhino.
My bet is that there are many more igneous fossils than archaeologists and geologists realize. Researchers just need to look for them in the right places, in the right ways.
Death by fire, then frozen in time… now, that’s a dramatic way to go. If I’m ever killed on one of my trips to an active volcano, at least maybe I’ll end up as a cool museum fossil a few hundred years from now.