Tephra
Tephra is fragmented rock, mineral, and volcanic glass ejected into the air during an eruption. It ranges from fine ash to large blocks and bombs.
Volcanic eruption column: A rising mixture of volcanic gas, ash, and larger fragments produced by an explosive eruption. The column carries tephra upward before winds disperse it or gravity brings it down.
Tephrochronology: The dating and correlation of geological or archaeological layers using distinctive volcanic ash deposits. A tephra layer can mark the same moment in otherwise separate sediment records.
Pyroclast: A fragment of volcanic material produced by explosive fragmentation or ejected during an eruption. Tephra consists of pyroclasts deposited from the air.
Mazama ash: A widespread volcanic ash deposit produced by the climactic eruption of Mount Mazama about 7,700 years ago. Its distinctive tephra layer serves as a marker across parts of western North America.
Volcanic ash: Fine volcanic particles smaller than two millimeters across, formed from fragmented rock, crystals, or glass. Ash is tephra's finest size class and can travel farthest from an eruption.
Volcanic ash hazard: The danger to people, infrastructure, agriculture, and ecosystems from airborne or deposited volcanic ash. Fine tephra can disrupt health, transport, power, and water supplies far from a volcano.
Pyroclastic flow: A fast, ground-hugging current of hot gas and volcanic fragments moving down a volcano's slopes. Unlike airborne tephra fall, a pyroclastic flow transports fragments in a dense current.
Yellowstone Lava Creek Tuff: A widespread deposit from Yellowstone's Lava Creek eruption about 631,000 years ago. Its ash-flow and fall deposits preserve the scale of a major explosive eruption.
Lapillus: A pyroclast measuring between two and 64 millimeters across. Lapilli show how tephra size classes distinguish fine ash from larger fragments.
Volcanic ash advisory: An official notice describing volcanic ash in the atmosphere and its potential effects on aviation. Advisories track airborne tephra that can damage aircraft engines.