Nuee Ardente and the Ignimbrites EarthCache
Hidden : 2/15/2018
Difficulty:
2 out of 5
Terrain:
2.5 out of 5

Size: Size: other (other)

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Geocache Description:


The title sounds like the name of a Greek rock band. In all actuality.....it is just the opposite. Not a Greek rock band but.....Greek for a band (flow) of rock.

The Flow:
A nuee ardente, more commonly known as a pyroclastic flow, is a superheated, fast moving, ground hugging body/cloud of ash, rock, and gas ejected from an explosive volcanic eruption. These gravity driven flows, able to reach speeds of 700km/h, are the most deadly expressions of any volcanic event.

Formation:
An ignimbrite is the pumice-dominated deposit formed from the cooling of a pyroclastic material flow. As the pyroclastic material settles it often builds up, creating thick layers which, if the temperature is sufficiently high (> 535°C), can weld (compact) into rock. The degree of welding depends upon the weight of overlying material, such that near the top of these deposits, the rock is commonly vesicular (containing small cavities produced by gas bubbles) and of low density. At depth the overlying weight crushes the pyroclastic material forming a dense, non-vesicular rock. While most volcanic rocks are found close to the source, ignimbrites of reasonable thickness can often be found hundreds of kilometres from the site of eruption.

Welded

Characteristics:
In general, ignimbrites are light colored.....pinkish white, pale grey. Darker colored ignimbrites may be composed of densely welded volcanic glass fragments. Overall, the mineralogy of an ignimbrite is basically controlled by the chemistry of the source magma. Its texture, if not welded, is aphanitic.....meaning its component minerals are too fine to be seen by the naked eye. If welded, it can be eutaxitic, which means it is layered or banded. Ignimbrites may contain lithic clasts (pieces of other rocks) and/or phenocrysts (conspicuous crystals distinctly larger than the grains of the rock groundmass itself). The term “ignimbrite” (from the Latin igni- "fire" and imbri- "rain") was originally coined by the New Zealand geologist Patrick Marshall in 1935. This term includes all pyroclastic flow deposits, no matter whether they are welded or not.


poorly welded

Since this is a dirt/gravel road, rain and snow at this altitude can change road conditions within minutes. In places this road is single lane and there are shear cliffs with no guard rails to protect you. Please park at 1 of 2 pull-outs near the site to allow traffic to pass safely. Drive slowly and carefully. Enjoy the views.

Email your answers to the questions, to me, by clicking on my name above. If your answers are not received by me, your log might be deleted as per GC rules. Photos are accepted and appreciated as long as the answers to the questions are not pictured. You do not have to wait for confirmation from me before logging this cache as completed. Most of all……learn……and enjoy the view.

1. In your opinion.....is this "flow" vesicular or non vesicular?
2. In your opinion.....is this "flow" aphanitic or eutaxitic?
3. Does this "flow" contain lithic clasts and/or phenocrysts?
4. In your opinion....is the "flow" welded or poorly welded?

Placement permission given by
Joe Huot
Special Projects Manager
Yavapai County Public Works
928-771-3183
928-771-3167 fax

Additional Hints ()

[Just before entering the Jerome Gold King Mine Ghost Town (from Jerome), turn right onto Jerome-Perkinsville Rd and start your uphill dirt road climb. This can also be accessed from Chino Valley or from Drake, both being much longer (30 plus miles of dirt road) but much more scenic drives. Approximately 4 miles once you leave blacktop in Jerome.]

Decryption Key

A|B|C|D|E|F|G|H|I|J|K|L|M
-------------------------
N|O|P|Q|R|S|T|U|V|W|X|Y|Z

(letter above equals below, and vice versa)

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