Wednesday, December 31, 2014

What a Geologist Sees - Part 18

Is this the world's smallest volcano? Maybe. [See the rock hammer for scale.]

This is a small example of a volcanic spatter vent. Usually spatter vents are late-stage events in the life cycle of an eruption, as the volcano is "losing its punch."

This spatter vent and the spatter mound shown below are just a couple of small, yet interesting features of the Aden Basalt Flows, which are part of the Potrillo Volcanic Field in southern Doña Ana County, New Mexico. The cinder cones of the northern parts of the Potrillo Volcanic Field are visible to the south of I-10, west of Las Cruces, New Mexico. Kilbourne's Hole, discussed in What a Geologist Sees - Part 13, is also part of the Potrillo Volcanic Field.

Most of the Aden Basalt flows are the result of fissure eruptions (lava flows erupted from open fractures in the ground surface), except in the northwestern part of the Aden Basalts, where Aden Crater (a small shield volcano) is present. Aden Crater is thought to have formed after the bulk of the fissure eruptions. Aden Crater (the subject of a future post) lies at the probable intersection of the Robledo Fault and the Aden Volcanic Rift (a buried fracture zone).

Spatter vents erupt by spitting small to moderate clots of partially solidified basalt (of the consistency of taffy).

The lower photo is of a mound of spatter material within Aden Crater itself. The stadia rod (used in mapping), leaning against the right side of the spatter mound, is about 6 feet long (for scale).

These are just a few of the many interesting volcanic features to be found in the Aden Basalts. Many typical features of basaltic vulcanism are preserved in the Potrillo Volcanic Field, along with some oddities that have not been seen elsewhere (for another post).

In another future post, I will show some different types of volcanic "ejecta" (aka volcanic bombs), which are found associated with some of the volcanoes of the Potrillo Volcanic Field. Just a suggestion, if you ever drive out into this area, carry plenty of water, have a good map, and let someone know where you are going.

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