Day 2
Walnut Canyon and Sunset Crater Volcano
Allie Gale
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Our first stop was at Walnut Canyon National Monument, just a few miles outside of Flagstaff. We were greeted by a magnificent overlook of the canyon as it was early (8:00 a.m.) and the sun was casting beautiful shadows. In addition, a friendly Student Conservation Association intern met with us to briefly describe the history of Walnut Canyon and its inhabitants.
First, we discussed the geology of Walnut Canyon. Beds of Kaibab limestone that now form the canyon's rim were at one time on the bottom of a warm, shallow ancient sea. This explains the mystery of seeing fossil shells and sponges along a trail that is now almost 7,000 feet above sea level! As the creek cut deeper into the canyon, the beautifully cross-bedded Coconino sandstone formation was exposed. It was in this formation 225 million years ago that strong winds blew across massive coastal sand dunes. This combination of a cutting creek and soft limestone interbedded with more resistant layers created the characteristic overhanging ledges. In addition, there has been new speculation regarding previously faulted blocks within the Kaibab limestone. This faulting pattern perhaps enabled the rock to weather and spawl off in chunks, creating larger caves. These ledges later provided natural apartments for the canyon's inhabitants. It has taken nearly 60 million years for the river to carve the canyon which is twenty miles long and 400 feet deep. Somewhat ironically, there was only one brief period (a few generations) when people lived in the canyon. At present, the river is dry and has not been active since the early 1900's.
Approximately 3,000 to 4,000 years ago, the earliest people began moving into the canyon. Their only remains are hand-size figurines left in a cave more than 3,000 years ago. Some investigators think the split-twig figurines may have been part of an early hunting ritual. Then following the eruption of Sunset Crater Volcano in A.D. 1065, the Sinagua Indians moved into the canyon. In the mid-1100's, the Southwest was undergoing a period of climatic fluctuations. The availability of water in the canyon perhaps influenced their decision to settle. Farming was risky and often unproductive; the Sinagua had to be resourceful. Corn was a main staple of their diet, although they also raised squash and beans. It is estimated that between 100 and 300 Sinagua lived here at one time, and stayed for a period of 150 years. There is some question as to why the people slowly abandoned Walnut Canyon although ideas include poor soil, drought or disease. After they left for good around 1250, the canyon was abandoned until the whites began exploring it in the 1800's.
The whites found beautiful pottery, ancient dwellings and even some mummified hands of the ancient people. Sadly, their interest led to greed and destruction. Looting of the cliff dwellings took a serious turn when pothunters began dynamiting the walls to let in more light. Finally in 1915, Woodrow Wilson proclaimed Walnut Canyon a national monument.
Differences in sun exposure and altitude create an abundance of plant species diversity near the canyon. Intense sunlight hits the south-facing slop and cactus, yucca and juniper are visible. In contrast, the shady north-facing slope is cooler and moister as evidenced by the presence of the ponderosa pines and Douglas firs. Pinyon pine nuts, as well as yucca fruits and the Arizona black walnut were a valuable food source for the inhabitants of the canyon. The Abert squirrels also may have been eaten, although they also played a vital role in the forest ecosystem.
Once we had heard about the natural history of Walnut Canyon, it was on to the hike! The Island Trail descends steeply into the canyon, dropping more than 200 feet and 240 steps; we were up to the challenge. The trail circles a ledge where Indian masons built many of their cliff houses. Along the way, we observed the beautiful cross bedded sandstones, the remnant fossils in the limestone and the cliff dwellings themselves. Although the dwellings seemed a bit small, it helped to keep in mind that the Sinagua men averaged five and a half feet in height and the women were a few inches shorter.
The fun didn't stop there however! At approximately 10:30 we loaded the vans and headed to our next stop: Sunset Crater Volcano. Luckily, Herbert Hoover proclaimed Sunset Crater Volcano a national monument in 1930. It was difficult for me to hide my excitement; the relatively recent eruption of Sunset Crater meant lots of cool lava rocks and formations. The subtle but highly variable color palette of the lavas surrounding the crater was astounding and reminiscent of a sunset. Sadly, no photo does this volcano justice!
At this stop, we didn't have a tour guide. We were free to hike the one-mile Lava Flow Trail at our leisure. However, it is important to briefly describe the volcano's history, beginning with the eruption! Earthquakes rocked the east side of the San Francisco Peaks for a week in the autumn of 1064. Finally, one day the ground swelled and a fissure opened. A cloud of ash swirled into the atmosphere and lightning broke through the darkness. Molten rocks were thrown out of the vent, and relatively low viscosity lava oozed outwards. The rain of cinders soon began to build a small cone around the vent. Through months of persistent eruption the cone grew until it stood a thousand feet above the surrounding land. This cone came to be known as Sunset Crater Volcano. To date the volcanoes, a process known as dendrochronology (or tree-ring dating) was used. Other radiometric dating methods are ineffective for such a short time span.
"Strombolian" is the class of eruption in which Sunset Crater is placed; in strength and explosiveness it is in the mid-range. To create a volcano, two things are needed: a mass of molten rock (called magma when it is below the surface) and a break in the ground. The magma from Sunset Crater was primarily basalt, a mafic rock rich in iron and silica poor. Hot lava flowed from the base of Sunset, in rough blocky chunks called aa. Lighter ash was blown miles away, blanketing the countryside. Altogether, more than a billion tons of lava, cinders and ash were produced that spread over 800 square miles of northern Arizona!
With this, hopefully we can begin to understand the magnitude of volcanic eruptions. Interesting studies have taken place regarding the eruption of Sunset; it is not considered to have been a single event but rather took place over the course of about 130 years. Because of the relatively small amounts of precipitation in the region however, Sunset Crater still preserves the look of a recent lava flow. Though gorgeous, locals are comforted by the idea that the chances of it erupting again are close to none.
The lava flow trail took us through all sorts of astounding structures including: pit craters, fumaroles, spatter cones, collapsed lava tubes, purple and blue boulders marked with vesicles of all sizes, miniature volcanoes, and even dramatically contorted trees! A lava tube forms due to differential cooling. The lava at the surface cools faster and skins over, while the lava underneath flows away, forming a hollow lava tube. Dr. Merck told us a few anecdotes about his adventures as a young boy visiting Sunset with his father. In those days, visitors were allowed to scramble up the side of the actual cinder cone! Dr. Merck was proud to say he had made it all the way to the top. In addition, there exists a so-called "ice cave" in the Bonito Lava Flow which is 225 feet deep (enough to support ice and snow year-round.) The fearless Dr. Merck climbed into the cave with his father some years ago. Sadly, due to the tremendous erosion caused by hiking the Crater Rim Trail it was closed to the public in 1973. One other neat thing was encountered along the way. We observed a tree with dramatic spiraling on its bark. What might have caused this, we wondered? Dr. Merck hypothesized that it had something to do with the tree rotating preferentially towards the greatest amount of sunlight. However, he and the rest of us weren't completely convinced. It is food for thought!
The first half of the day came to a pleasant close while eating a picnic lunch surrounded by friends near the magnificent Sunset Crater Volcano.
Sources:
Press, Inc. 15 pp.