Geology Word (Phrase?) of the Week: Volcanic Bomb

Hi everyone! Guess what? I’m posting again on human timescales. I have tried and failed (at least twice) in the past to regularly post a “Geology Word of the Week.” Third time is a charm, let’s hope! I’ll do my best to post a geology word of the week every Friday. I think I tried before on Mondays… Fridays might be better as it’s easier to justify procrastination at the end of the week.

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 neat pictures of volcanic bombs that I stole from the interwebs. I apologize if these pictures are a little cut off- eventually (*cough* when I finish grad school), I’ll stop being too lazy to re-size images.

I am 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.

Just a hint (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? That 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!


Evelyn is a geologist, writer, traveler, and skeptic residing in Cape Town, South Africa with frequent trips back to the US for work. She has two adorable cats; enjoys hiking, rock climbing, and kayaking; and has a very large rock collection. You can follow her on twitter @GeoEvelyn. She also writes a geology blog called Georneys.

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  1. Very cool…I know next to nothing about geology so I’m looking forward to the word of the weeks! But I’ll be forgiving if grad school gets in the way ;)

    Loved the airport story

  2. I think the future geologists are going to be too busy wondering about the metamophosed skyscrapers and rubbish dumps to notice your volcanic bomb.

  3. Thank you so much for posting. I love that I can come to skepchick and learn a bit about GEOLOGY! I truly appreciate the diversification you bring to this site. And it’s GOOD diversification!

  4. Actually, just don’t say the words “seismic” or “volcano”.

    In the early 90’s, coming back from Costa Rica on a Smithsonian funded trip (you know, that world famous organization that issued freakin’ diplomatic passports to my mentor and his assistant), they took one of the staff members aside because they didn’t like the look of our seismic equipment and decided to grill his butt about it. The big old “scientific equipment” stickers along with the Smithsonian stickers were of no help. The sad thing was, this was coming BACK – on the way there, Costa Rican customs didn’t even bat an eye.

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