The Hornsby Volcano - Maar Volcanoes and Diatremes

[Hope things have settled a bit for you, from this wild, wild year.]

After posting scads of Arkansas Diamond-related videos, perhaps it's time to look at Diatremes (the "host rock") and their sometimes-companion Maar Volcanoes.  The host rock for the Crater of Diamonds Park is termed by some as the Prairie Lake Diatreme.  

It seems there aren't many such videos, at least that I have found.  The above video is from Australia.  At about 1:50 in the above video is the discussion of the Maar-Diatreme "combo" for this particular locality.  In another Australian video, the narrator describes Maar-Diatreme combos beginning at about 1:45.  

A U.S. National Park Service post about Maar-Diatreme combos is here.  In the heavily-eroded Navajo Volcanic Field in NE Arizona and adjacent NW New Mexico, there are some occurrences of maars and diatremes, including the Buell Park Diatreme in Apache County, AZ northwest of Gallup, New Mexico.

A maar is a low-relief crater caused by a phreatomagmatic eruption. This is a situation where groundwater comes in contact with lava or magma and the resulting steam causes an explosion. This digs out a hole in the ground, creating the maar crater. And then, it usually fills back in to create a lake.

Kilbourne Hole is one of several volcanic maars located in Doña Ana County, New Mexico. Volcanic maars are unusual volcanic features, and Kilbourne is probably the best example to be seen anywhere in the world. Maars look something like meteor impact craters, but they are formed by other processes.

The theory of maar formation is that rising magma super-heats water-saturated earth (as with an aquifer), far enough below the surface that the high pressure can be contained.  At some point, the pressure is too much, and a steam explosion occurs, throwing the earth out in a catastrophic event.  Country rocks are fragmented and expelled in the atmosphere (together with fragments of the magma), in phreatic explosions that  - among those observed - last weeks to months before the eruptive energy subsides.

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Kilbourne Hole is roughly elliptical in shape and is known as a Maar — a pit or depression caused by a volcanic explosion with little material emitted except volcanic gas. The crater is between 24,000 and 100,000 years old, and measures 1.7 miles long by well over a mile across, and is hundreds of feet deep.

In Rio Grande Rift references, other maars have been mentioned, but those await coverage at another time.