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National Geographic : 1960 Oct
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National Geographic, October, 1960 and through the little town of Arco. To the north the brooding Pioneer Mountains and the Lost River Range climbed sharply (map, opposite). To the south a silent wilderness of lava and pale greenery blended into shim mering heat waves. Then I saw a mass of black rocks rising from the plain, stretching like an enormous flattened-out coal pile as far as I could see. I sensed that something fearful, something cataclysmic had happened here. My wife Fran and our lively teen-agers, Buzz and Loie, were studying a pamphlet about the monument. "Like walking on the moon," it read, above a picture of little men in fish-bowl helmets. Loie could hardly wait. We had barely left Superintendent Hender son's house near the visitor center and driven to a parking spot along the Loop Drive, when we sighted an odd shape stirring in a depres sion in the lava rock. It looked brownish green and gave off clanking noises. Loie was KODACHROME© NATIONALGEOGRAPHICSOCIETY speechless. Closer approach revealed a husky, sunburned man in khaki, wearing a green can teen belt, who was cutting samples with a rock hammer. He was John Murtaugh, a young geologist from the University of Idaho, map ping the Great Rift lava flows under a grant from the National Park Service. "This place is still full of questions," Mur taugh said. "For one thing, how many lava flows were there? Compared to other classic areas of volcanism-Iceland, Italy, Japan, Hawaii-Craters of the Moon gets little rain, only about 10 inches a year. And moisture initiates the breaking down of lava. Because there is so little rainfall here, some of the flows look deceptively fresh." Minerals May Help Classify Flows Murtaugh recalled that Dr. H. T. Stearns, a geologist who studied the area three decades ago, listed 27 flows in two discernible ages. Stearns surmised that there may have been a third age, the earliest. "The older flows presumably were covered by later eruptions," Murtaugh said. "All the lava probably came from the same under ground reservoir. But each of those three ages may have lasted a thousand years; in the intervals the composition of the magma may have changed. My samples will be tested to discover what minerals are present and in what proportions. Those proportions may differ and help us classify the flows." But how long ago did the flows start, and when did they end? "That's the toughest question of all," Mur taugh replied. To early ranchers the lava looked fresh. Charred tree trunks near by reinforced their idea that this flow must be very young, perhaps 100 years or less. But then came doubts: Had those trees been scorched by prairie fires, not lava? "Now we know that the flow we're stand ing on is one of the youngest in the monu ment, and it is more than 1,600 years old," Murtaugh said. "Our evidence is right over there." "Nonskid tire tracks" mark a molten river's passage through a forest some 1,600 years ago. Lava, igniting a fallen tree like a torch, retained the impres sion left by the shrinking sapwood. A visitor on the Blue Dragon Flow in spects the pattern, strikingly like that of a truck tire. 508
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