To date the volcano dendrochronology, also known as tree ring dating, must be used. This is because radiometric dating methods are ineffective for a site that is relatively young. The volcano here first started erupting in 1064 AD. First, magma emerged from fissures and eventually form a cone shape. The top of the cone would accumulate more gasesous magma than the bottom. Eruptions of cinders would follow, which covered approximately 800 square miles and nourished the surrounding land. Then fissures formed around the base of the cone, transporting frothier, less viscous, magma. The final eruption of the volcano was about 700 years ago in 1250 AD.

Our group walked the Lava Flow Trail which showed much information about the geological formations. The rocks here are dark, igneous rocks made up basalt and volcanic ash. One of the first things we saw was a lava tube. A lava tube forms when the lava at the surface, where the temperature is cooler, skins over. The lava underneath still flows and can completely flow away, forming a hollow lava tube. Next we saw hardened aa flow, which has a jagged, blocky, appearance. The ropy lava flow called pahoehoe is much harder to find here. Moving along the trail, we saw a spatter cone. A spatter cone is like a miniature volcano that is built up around a fumerole, where gases escape from lava. The last thing we saw was the Ice Cave, a 225 foot long cave with ice in it. Dr. Merck told us how in 1966 he was allowed to enter the cave when preservation measures were not as strong as today. Now the cave is closed by gates. The group at lunch at while fighting the winds before leaving for Walnut Canyon.

We arrived at Walnut Canyon around 1:45 PM. The thermometer there read 39 degrees Fahrenheit. Walnut Canyon is the Site of abandoned Sinagua Native American cliff dwellings. The site got its name from the Arizona Black Walnut trees that grow in the bottom of the canyon. The Coconina sandstone made from sand dunes of 280 million years ago is easily visible in the bottom half of the canyon. Above that, the Kaibab Limestone from an ancient inland sea from 20 million years ago can be identified. Walnut Creek is currently dry and has not been running since the early 1900s.

One of the staff members named Linda gave us a tour of the site. She told us that the Sinagua abandoned Walnut Canyon about 800 years ago. After descending several hundred stairs we came upon the first grotto of the trail. Linda informed us that this grotto was used for storage. The Sinagua would have packed food in jars along with snow, then put the jars in these storage areas to keep the food preserved. We know which grottos were used as dwellings because they have smoke stains on the ceiling. Also, some dwellings have a small door with a hole above for ventilation of smoke. As we walked along the path, snow flurries began to come from the sky. We got first hand experience of the dwellings effectiveness as shelter. We felt as the ancient Sinagua might have during bad weather. The trail made a loop back to where we started, so we climbed the stairs back to our vans. There we drove our hotel so we could eat dinner and rest after a long day.

More information about Sunset Crater can be obtained at http://www.nps.gov/sucr/.

More information about Walnut Canyon can be obtained at http://www.nps.gov/waca/.

Sources:

Dr. Merck

Dr. Holtz

"Lava Flow Trail Guide" from Sunset Crater Volcano National Monument

Day 4 - Boyce thompson Arboretum and a long road trip
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