February 02, 2010
Volcanic bombs are blobs of lava that have been ejected from a volcano during eruption. Being somewhat gooey, airflow often molds them into aerodynamic shapes, producing teardrop or flying saucer shapes. Some bombs cool and harden before hitting the ground; however, this one was still viscous, and its sharp leading edge (left) was curled over on impact. The airflow lines and direction are clearly evident on the bomb’s surface, indicating that it was oriented and not tumbling through the air. Like most lava, this one contained dissolved gas which came out of solution and formed bubbles.
Bombs can be thrown many kilometers from a vent, but this one probably traveled only a few hundred meters, which perhaps explains why it did not have time to cool before landing. It was found on a cinder cone on the south flank of Mauna Kea, on the Big Island of Hawaii, where many other bombs could be seen.
See also: Field Guide to the San Andreas Fault
Earth Observatory images: