A vocabulary of landscape — a landscape of words
1190 entries
diatreme
A diatreme is a volcanic pipe drilled straight up through the crust by gas-charged magma, producing a narrow carrot-shaped body of shattered rock rather than a lava flow or a cone. The eruption is explosive and brief, driven by expanding gas rather than by the heat of the melt, and it can move material upward at supersonic speed. Once the surrounding rock erodes away, what remains is a plug standing on its own.
Etymology
The word is Greek for a hole bored through, and it was created for the purpose in the nineteenth century as geologists worked out that some volcanic necks had been drilled from below rather than filled from above. It belongs to a family of terms in which the Greek does the descriptive work that plain English would make clumsy: A maar is the crater at the top of one, and a tuff ring is the low rim of ejected material around it.
Notes
Diatremes are how diamonds reach the surface. Kimberlite pipes are diatremes that started deep enough in the mantle to carry diamond up faster than the carbon could revert to graphite, which requires an ascent measured in hours. Ship Rock in New Mexico and Devils Tower in Wyoming are eroded volcanic necks of related kinds, standing where the softer rock around them has gone.