Because it was feared that fine particles of tephra in the ash cloud would cause jet engines to fail, the eruption led to a six-day closure of European airspace, causing airlines to lose more than $250 million daily.
In western North America, Pleistocene tephra (those from 11,700 to 2.6 million years old) have been correlated over a distance greater than 1,600 km (1,000 miles).
The term tephra as originally defined was a synonym for pyroclastic materials, but it is now used in the more-restricted sense of pyroclastic materials deposited by falling through the air rather than those settling out of pyroclastic flows.
For example, ash particles that fall from a high eruption cloud to form widespread layers downwind from a volcanic eruption are referred to as tephra and not as a pyroclastic flow deposit.
Over the course of the event, Novarupta ejected about 28 cubic km (about 6.7 cubic miles) of tephra (ash particles that later fall) some 32 km (20 miles) into the stratosphere.
Tephrochronology, method of age determination that makes use of layers of ash (tephra).
In volcanic regions tephra (erupted ash) may also contribute to soil depth and fertility.
In tephrochronology, layers of volcanic ash, tephra, often contain potassium-bearing minerals whose crystallization age can be determined, even going back billions of years.
It has been some while since the amphitheatre at Pompeii hosted any kind of audience – AD79, in fact, when Mount Vesuvius erupted and buried the ancient city five metres deep in tephra, only to lie undisturbed until the 18th century.
The volcano, located deep in the Sahara desert in the Fezzan region of southwestern Libya, appears as a smear of dark basaltic ash and tephra that contrasts sharply with the light-coloured sand of the Sahara.
South of the ash field, mud streams have begun the slow process of eroding the tephra and ash away.
