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

Note: I started the Geology Word of the Week at Skepchick, where I am one of several fabulous, skeptical women (and one deserving man) bloggers. For the first few weeks of the Geology Word of the Week, I am going to re-post my "Geology Words of the Week(ish)" from Skepchick. Before being distracted by graduate school and life, I made my way from A to G... I will re-post those letters here and then continue with the rest of the alphabet. In 26 weeks, I will have made my way through the alphabet!

For this week's word starting with the letter b, I am reposting my Skepchick post about bombs. Volcanic bombs, that is. I have modified my previous post slightly to better fit with the formatting for this blog, but the content is the same. Note that I also blogged at Skepchick about the the word Burdigalian. However, since I am traveling to volcano-filled Costa Rica tonight, I thought I would re-post the volcanic word.

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.