Tephra refers to air-fall material produced by a volcanic eruption regardless of composition or fragment size. Tephra is typically rhyolitic in composition as most explosive volcanoes are the product of the more viscous felsic or high silica magmas. Eruption redirects here. ... Rhyolite Rhyolite is an igneous, volcanic (extrusive) rock, of felsic composition, with aphanitic to porphyritic texture. ... The pitch drop experiment at the University of Queensland. ... Felsic is a term used in geology to refer to silicate minerals, magmas, and rocks which are enriched in the lighter elements, such as silica, oxygen, aluminium, sodium, and potassium. ... The chemical compound silicon dioxide, also known as silica, is the oxide of silicon, chemical formula SiO2. ... Magma is molten rock often located inside a magma chamber beneath the surface of the Earth. ...

Volcanologists also refer to airborne fragments as pyroclasts or sometimes just clasts. Once clasts have fallen to the ground they remain as tephra unless hot enough to fuse together into pyroclastic rock or tuff. The distribution of tephra following an eruption usually involves the largest boulders falling to the ground quickest and therefore closest to the vent, while smaller fragments travel further - ash can often travel for thousands of miles as it can stay in the stratosphere for several weeks. Pyroclastic rocks and deposits comprise the entire range of fragmental products deposited directly by explosive or effusive volcanic eruptions. ... Welded tuff at Golden Gate in Yellowstone National Park Tuff (from the Italian tufo and pronounced tuf) is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. ... The stratosphere is a layer of Earths atmosphere that is stratified in temperature, with warmer layers higher up and cooler layers farther down. ...

Trephra fragments are classified by size:

• Ash - particles less than 2 mm in diameter
• Lapilli or volcanic cinders - between 2 and 64 mm in diameter
• Volcanic bombs or volcanic blocks - greater than 64 mm in diameter

The words "tephra" and "pyroclast" both derive from Greek. Tephra means "ash". Pyro means "fire" and klastos means "broken"; thus pyroclasts carry the connotation of "broken by fire". Diamond Head, a well-known backdrop to Waikiki in Hawaii, is an ash cone that solidified into tuff Volcanic ash is the term for very fine rock and mineral particles less than 2 mm in diameter that are ejected from a volcanic vent. ... Lapilli are small particles of solidified lava (tephra) thrown into the air by volcanic eruptions. ... Volcanic bombs are globules of melted rock (tephra) larger than 2. ...

The use of tephra layers as temporal marker horizons is known as tephrochronology. Tephrochronology is a geochronolgical technique that utilises discreet layers of tephra—volcanic ash from a single eruption— to create a chronological framework in which palaeoenvironmental or archaeological records can be placed. ...

External links

• How Volcanoes Work
• Volcanic Materials Identification