Tephra, the Greek word for ash, is used to describe any material that is ejected by a volcano into the atmosphere (pyroclasts). Tephra includes dense blocks and bombs (> 64 mm), and lighter materials such as scoria, pumice and ash (< 2 mm). As one moves away from a volcano, the tephra deposits become finer grained (smaller particles) and thinner. This is because small airborne particles hover longer and stay within the atmosphere for a greater distance from the volcano. These particles of ash …