Red Mountain Volcano EarthCache

You will need a compass to be able to record these. If you GPSr doesn't have one please bring one along as it is the only way to orient yourself to see the features mentioned in the Waypoints.

This Earthcache is located at Red Mountain volcano, AZ.

We personally have been to this place many times and wondered at its geology. Now you too can come and enjoy one of Northern Arizona's natural wonders. This Earthcache is located right on the way to the Grand Canyon from Flagstaff, AZ.

Red Mountain, located in the Coconino National Forest of northern Arizona, 25 miles northwest of Flagstaff, is a volcanic cinder cone that rises 1,000 feet above the surrounding landscape. It is unusual in having the shape of a "U," open to the west, and in lacking the symmetrical shape of most cinder cones. In addition, a large natural amphitheater cuts into the cone's northeast flank. Erosional pillars called "hoodoos" decorate its amphitheater, and many dark mineral crystals erode out of its walls. Studies by U.S. Geological Survey (USGS) and Northern Arizona University scientists suggest that Red Mountain formed in eruptions about 740,000 years ago.

Red Mountain is unusual in that its internal structure is exposed. This is not the case at most cinder cones in the San Francisco Volcanic Field, because erosion has not had enough time to expose their internal features. Although human quarrying creates frequently changing glimpses into a few of the cones in the volcanic field, quarries generally are unsafe for tourists and public access commonly is denied.

Near Red Mountain a large Forest Service sign along Highway 180 invites the motorist to exit and visit this cinder cone. A parking lot is located about a quarter mile off the highway. A gentle, uphill, 30-minute walk from the parking lot brings the visitor into a natural amphitheater carved into the northeast flank of Red Mountain. The back wall of the amphitheater is a nearly vertical 800-foot cliff, which tapers off to the right and left. Truncated layers of volcanic cinders form ledges and color bands across the amphitheater walls.

An "ideal" cinder cone forms when eruption occurs on flat ground. From deep within the Earth, magma charged with gas (like a carbonated drink) rises through a vertical pipe-shaped conduit and erupts as a fountain of frothy lava that may spray as high as 2,000 feet into the air.

As an individual blob of this frothy molten rock flies through the air, it cools quickly enough to solidify before falling back to Earth. Many gas bubbles remain trapped in the fragments. If small, these fragments of rock are called "cinders," and if larger, "bombs."

As eruption continues, cinders accumulate to form a conical hill. Periodically, the flanks of the growing hill may become so steep that lobes and sheets of cinders slide downward. When lava fountaining ends, a symmetrical cone-shaped hill, commonly indented by a summit crater, has been added to the landscape. Internally, the cone is a pile of loose cinders in layers that dip away from the volcano's vent in all directions.

During the waning stage of an ideal cinder-cone eruption, the magma has lost most of its gas content. This gas-depleted magma does not fountain but oozes quietly into the crater or beneath the base of the cone as lava. Because it contains so few gas bubbles, the molten lava is denser than the bubble-rich cinders. Thus, it burrows out along the bottom of the cinder cone, lifting the less-dense cinders like a cork on water, and advances outward, creating a lava flow around the cone's base. When the eruption ends, a symmetrical cone of cinders sits at the center of a surrounding pad of lava.

Origin of the Amphitheater

The origin of the Red Mountain amphitheater is something of a geologic mystery. The truncated cinder layers exposed in the amphitheater walls are clear evidence that material has been removed. However, how this removal was accomplished is not entirely clear.

It seems unlikely that the entire amphitheater was created by water erosion, because there is so little surface area to catch rainwater and snowmelt and funnel it down channels to erode the side of the volcano. An intriguing, though speculative, possibility is that one or more steam explosions created an amphitheater-shaped hole in the side of Red Mountain shortly after eruption ceased. Newly erupted cinders probably cooled to about 600° F as they fell back to earth, but then remained well above the boiling temperature of water for some time. Rainwater seeping into the cone and circulating through the still hot cinders may have quickly deposited a strong mineral cement that bound cinders together, creating the equivalent of a sealed "pressure cooker." Eventually, the pressure of the trapped superheated water may have exceeded the strength of that cooker, resulting in one or more steam explosions.

The stream sand on the way to the amphitheater includes countless black shiny grains, a few as large as walnuts.

These grains are sometimes mistaken for "Apache tears," which are composed of obsidian, the volcanic glass highly valued by ancient cultures for crafting arrowheads, knives, scrapers and other tools. However, the abundant black grains at Red Mountain are crystals of minerals (pyroxene and amphibole) eroded from the volcano. A close look at the walls of the amphitheater will reveal crystals of these minerals still embedded in cinders, waiting to be plucked out by water and wind erosion.

The amphitheater of Red Mountain has many "hoodoos" rather bizarre landforms that are especially common in the western part of the amphitheater These 10- to 20-foot-tall, upward-tapering earth pinnacles of cinders are capped by 1- to 3-foot-wide boulders of dense lava. The boulder "sombrero" capping each pinnacle (see above) protects the underlying cinders from erosion. These hoodoos and other odd-looking spires, ridges, and ribs found in the amphitheater were almost certainly sculpted by water and wind erosion.

To log this EarthCache:

To receive credit for this Earthcache you must answer questions for the following waypoints. You will need a compass to be able to record these. If you GPSr doesn't have one please bring one along as it is the only way to orient yourself to see the features mentioned in the Waypoints.

Waypoint 1
Describe the shape of Red Mountain from this distance, it is to the Southwest

Waypoint 2
What is the hill to your Northwest made off? What is in the stream bed at your feet?

Waypoint 3
What is this structure called?

Waypoint 4
What is under your feet?
What do you think made the holes in the wall to your Northwest?

Waypoint 5
What is this object called?

Explore and have fun but be careful. The amphitheater is a beautiful place but there are some drop-offs. Watch little ones closely.

Leave No Trace Techniques for Geocaching 

The essentials of responsible geocaching:

• Never bury caches.

• Never leave food items in a cache.

• Replace rocks & other natural objects lifted during a search.

• Find routes that minimize impact.

• Leave places looking as if the seekers had never been there.

Enjoy the cache and have fun. Please replace it exactly as you found it so that others following you can find it exactly as intended.

Enjoy this Earthcache and have fun.

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