National Geographic : 1978 Jul
bother some visitors. Not only do they "mask the natural sounds," the study claims, but they also impede communica tions between boat operators and passen gers-preventing safety warnings. Com mercial motorboat operators counter that the motors do no damage and permit them to carry more people faster, cheaper, and more safely than oar-powered trips. When the Colorado ran free, an average of 380,000 tons of silt passed the gauging sta tion at Phantom Ranch every day. During a 1927 flood, 27,600,000 tons were recorded one day. Now there are about 40,000 a day, and no major floods. The rest is collecting in Lake Powell. The water no longer deposits sand but slowly hauls away beaches already there. Since the reduced flows can no longer clear debris brought down side canyons, rapids will get worse. At Phantom Ranch, 90 miles upriver from Lava, I had talked with another Roy. Roy Starkey works for the ranch. He used to work for the U. S. Geological Survey. "For 20 years I took water samples and checked flow and temperature every day," he said. "But I lost my job to a satellite." An automatic "fish" now tests the river every morning. A solar-powered radio transmits the data directly to a weather sat ellite over Brazil, which relays it to a Virgin ia receiving station, which automatically telephones it to the Geological Survey com puter at Reston, Virginia, for processing. All of this happens each morning faster than Roy can turn off his alarm clock. SON SMITH returned to our river camp to report that the water wouldn't come up for several days. Roy Johnson and I de cided to pack out. Fortunately for us, one of the few escape routes out of the canyon starts just above Lava. It follows a gully in a near-vertical 3,000-foot slope of loose black volcanic cin ders. Under summer sun the surface tem perature may reach 200°F. In March it was no problem, except that at times it was like going up a vertical treadmill. The trail seemed determined to slide to the river faster than we could go up. The slope continued on 600 feet above the Toroweap Valley floor to form a textbook-perfect volcanic cone called Vulcans Throne. A series of eruptions some Grand Canyon:Are We Loving It to Death? 10,000 years ago formed the cone and near by lava cascades (page 48). Volcanism was no stranger to the canyon here: At several intervals beginning more than two million years ago, lava poured into the chasm, forming dams as high as 2,300 feet-high enough to create a lake reaching back beyond Lees Ferry, 179 miles up stream. The last lava dam, 80 miles long and perhaps 800 feet high, blocked the river about 250,000 years ago. After each dam was created, the lake would eventually breach the top of the black barrier and the river would resume its grind ing search for sea level, slowly wearing down and clearing the dam away. Our trail finally led us to the Riffeys' back door, and they took us in like the waifs we were. John Riffey knew, but avoided, our Big-as-salmon rainbows have invaded since Glen Canyon Dam upstream lowered river temperatures and trapped most of the silt. The cold water that the trout require could mean extinction for native species.