Mount Elden initially produced large gas explosions from hot ash and rocks scattered across the ancient landscape. As the ashes cooled, their texture formed tufa, a stone that was later quarried by the early Flagstaffians when they built some homes and businesses, such as the Pita Pit building on the southwest corner of Aspen Avenue and San Francisco Street.
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The amount of silica in a magma or lava determines its viscosity: the more silica there is, the more viscous it is. They have an average silica content of 65% to 70%. The smaller, nearby cinder cones like Sunset Crater erupted less viscous lava (called basalt, with an average silica content of about 50%).
In addition to Mount Elden, there are several other Dacite dome volcanoes in our area – Bill Williams Mountain (the oldest at around 6 million years old), Mount Sitgreaves, Mount Kendrick, Schultz Peak, O’Leary Peak, and Sugarloaf (the youngest at around 95 thousand Years). All of these dome volcanoes formed in a similar way and have similar types of rocks. But they erupted at different times, with the older domes generally being in the west and the younger ones being in the east. Mount Elden erupted about 500,000 years ago.
Earth view of Mount Elden, immediately north of East Flagstaff and Buffalo Park. Note the numerous lobes of Dacite lava that seeped down the southern and western flanks of the mountain and the bulging layers of sedimentary rock (the “trap door”) to the east and northeast of Elden.
Decency
Strangely enough, the lava on Mount Elden could not flow completely. As the hot, viscous lava piled higher and higher, its slopes were steepened, so that the hot lava began to creep very slowly downhill. Tongues (or rags) of lava are still visible today when flying over or around the mountain (see attached pictures). Although these lobes are half a million years old, their shapes are beautifully preserved. Lava with this viscosity must have had the consistency of toothpaste, which looked immobile overall, but crept imperceptibly downhill.
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