Noun
tephra (countable and uncountable, plural tephras)
(geology) The solid material thrown into the air by a volcanic eruption that settles on the surrounding areas.
An eruption in 1900 BCE was the largest known eruption from St. Helens during the Holocene epoch, judged by the volume of one of the tephra layers from that period. Source: Internet
Recent and ongoing projects include gravimetric and GPS-based geodetic monitoring, fumarole gas sampling, tephra distribution mapping, new interpretations of the Schriebers Meadow lava flow, and hazards analyses. Source: Internet
In this scenario the slopes of the mountain, extending out to about convert from the vent, may be exposed to pyroclastic flows sweeping down them, whilst much of the surrounding area could suffer from tephra falls. Source: Internet
The loose pile of unconsolidated tephra would quickly have been washed away had the supply of fresh magma dwindled, and large clouds of dust were often seen blowing away from the island during this stage of the eruption. Source: Internet
Similarly, by tephrochronological techniques, the lack of glacier cover can be identified by the presence of soil or volcanic tephra horizons whose date of deposit may also be ascertained. Source: Internet
The technique is not restricted to tree rings; for example, a stratified tephra sequence in New Zealand, known to predate human colonization of the islands, has been dated to 1314 AD ± 12 years by wiggle-matching. Source: Internet