November 10, 2010

Geology Word of the Week: B is for (Volcanic) Bomb

Posted by Evelyn Mervine

Fiesty Arenal Volcano, Costa Rica, June 2008.

This week’s geology word of the week is actually a phrase: volcanic bomb.

def. Volcanic Bomb:
A rock that forms when lava is thrown up into the air and cools very quickly. Volcanic bombs have characteristic shapes that they take on when they turn and twist in the air as they cool. They are often tear-drop shaped with a long tail. To be called a bomb, the tephra (another potential word of the week… this basically refers to material ejected by a volcano) must be greater than 64 mm in diameter. Tephra 2-64 mm in diameter is called volcanic lapilli while tephra smaller than 2mm is called volcanic ash.

Here are some links to some beautiful pictures of volcanic bombs:
Bomb #1

Bomb #2

Many more bombs!

I am posting links above because in this blog I want to make an effort not to steal photos off the internet. I want to give credit where credit is due. Unfortunately, I don’t have a good picture of a volcanic bomb in my personal collection of geology photographs. I think it’s time to visit some volcanoes…

I am, however, the proud owner of a volcanic bomb which I picked up from a volcano in California near Mono Lake. I acquired this rock during a geology field trip I went on as an undergraduate. After the field trip, I brought this rock to my parents’ house. My mom wouldn’t let me bring such a large rock inside the house, so I put it in my mother’s flower garden, where it still sits (next to some delightful pegmatite samples), certain to confuse future generations of geologists who will wonder where there are volcanoes in New Hampshire.

I was not the only one to pick up a volcanic bomb during this trip to California. We actually collected several, and we wrapped them in sleeping bags and put them in plastic coolers so that we could transport them back to New Hampshire safely. Just to make the coolers look as sketchy as possible for the TSA folks, we wrapped duct tape randomly around the coolers to keep them closed.

Here’s some advice (for a certain geology professor and everyone else): when transporting volcanic bombs via air travel DO NOT refer to the rocks as volcanic bombs. In fact, I’d go so far as to say that the words “volcanic” and “bomb” should never be uttered within an airport and certainly not in combination.

Here’s a (somewhat stylized through tricks of memory and artistic license) conversation that almost landed the entire geology field trip in a questioning room at the Las Vegas Airport:
TSA official: What’s in the coolers?

Naive geology professor: Oh, those are our volcanic bombs!

TSA official: Your WHAT?

Naive geology professor: Volcanic bombs. They’re great examples, very large bombs… that’s why the coolers are so heavy.

TSA official: Sir, I need to see your passport please.

Quick-thinking geology student: What Prof. Naive meant to say is that these are scientific rock samples from X volcano in California. We’re going to take them back to our college so that we can use these specimens as classroom examples. Would you like me to show you the samples? They are really beautiful rocks.

TSA official: Beautiful rocks? You mean these coolers are full of rocks?

Naive geology professor: Yes! Beautiful examples of volcanic bom–

Quick-thinking geology student: Yes, rocks. We’re geologists. We’ve wrapped the rocks in sleeping bags so that they don’t break. If they break it would ruin some really great scientific samples for very important scientific research.

TSA official: You’re worried about the rocks breaking? So you wrapped them in sleeping bags?

Naive geology professor: And duct tape! So many uses for duct tape. I hope you don’t want to see the bombs because the duct tape is hard to–

Second quick-thinking geology student: I’d be happy to open the cooler, sir. Let me just get the tape off…

TSA official: Okay, I’d like your group to step aside. We’re going to have to hand search all your luggage.

First quick-thinking geology student (Muttered under breath to second quick-thinking geology student): Don’t let Prof. Naive say anything else… ask him a question about crystallization phases or something…
Well, we did make it through security eventually and didn’t miss our flight. Again, let me repeat: do not use the phrase “volcanic bomb” in the airport. Fortunately, this incident happened several years ago before security became so crazy. I think today we would end up in the questioning room for sure.

That’s the word for this week… stay tuned for more geological tidbits! I’ll be back in a few days!