or passengers and boaters alike, Lava Falls Rapid is the highlight of most river trips through Grand Canyon. Who doesn't remember at least one thrashing in the V-Waves, or looking up at the Big Wave as it crashes over your boat? Even worse, some people have the memory of plunging into the Ledge Hole with its attendant consequences. In recent years, the rapid has changed, adding some new hazards as well as making the run easier at some water levels. After watching Brian Dierker recirculate in the Corner Pocket last March after a flip in the V-Waves, we were reminded of just how much Lava Falls has changed since John Wesley Powell first encountered the rapid in 1869.
Debate has raged since Powell's first trip about which rapids were the most severe in Grand Canyon. Powell made a big deal about the severity of Separation Rapid, using fear of the rapid as the reason that the Howland brothers and Dunn hiked out of Grand Canyon in Separation Canyon. Powell possibly exaggerated the size of Separation Rapid to create a diversion for the real reason the Howlands and Dunn left his trip: Powell's overbearing personality. Robert Brewster Stanton, who led the second expedition through Grand Canyon, thought Lava Cliff was the worst rapid he saw. In a 1976 paper, Otis “Dock” Marston, noted river historian, compared Lava Falls, Lava Cliff, and Separation rapids and decided the latter wasn't in the same league with the former two. We'll never really know whether Lava Falls or Lava Cliff was the most severe rapid, in part because Lava Falls has changed so much and Lava Cliff has been under Lake Mead since the late 1930s.

There is no doubt that Lava Falls has historically been a large rapid. However, most of its hazards are completely different from what the early expeditions saw and photographed. We've obtained 234 historical views of Lava Falls to date, and we've matched 121 of these to assess how the rapid has changed since April 1871, when it was first photographed by members of the second Powell Expedition. We used this evidence—plus river-runner movies, some scientific dating methods, and a lot of surveying—to reconstruct not only historical changes to Lava Falls, but also when prehistoric debris flows occurred and how big they were.
Why is the rapid where it is? Some observers have written that Lava Falls is controlled by underwater basalt dikes or the remaining base of lava dams. Both Powell and Stanton thought dikes to be the cause for the rapid. Interesting theory, given the rapid's position under the frozen cascades of basalt flows that inspired the name, but there is no evidence for underwater dikes in the rapid. Instead, if you look at the debris fan on river left, which towers about 75 feet over the rapid, you can see the smoking gun evidence of large debris flows from Prospect Canyon. Why is the rapid so big? The various waves and holes in the rapid are created by large boulders, most of which have only been in the rapid for fifty–sixty years. Many photographs taken at low water show these boulders above water level. A quick hike up Prospect Canyon will convince anyone that debris flows occur frequently in this canyon and transport extremely large boulders when they do.

After working fourteen years on debris flows in Grand Canyon, we've concluded that both the largest debris flow in the last 11,000 years (the Holocene) as well as the largest historical debris flow occurred in Prospect Canyon, and these were two different events. The largest Holocene debris flow occurred around 3,000 years ago and formed the large surface on the upstream side of the wash issuing from Prospect Canyon (see table below). This debris flow raised the bed of the Colorado River by 90 feet, at least temporarily. The largest historical debris flow occurred in 1939, and the 1939 deposits are dwarfed by the 3,000-year-old deposits. The 1939 debris flow didn't dam the Colorado River, but its debris fan constricted the river by about eighty percent.

A total of six debris flows have occurred historically in Prospect Canyon, and each changed the rapid, at least temporarily. The rapid that Powell and Stanton saw was wide with lots of exposed rocks in the middle of the river at discharges of less than 10,000 cfs. The rapid remained stable from 1869 until Don Harris and Bert Loper ran the rapid at 7,700 cfs in 1939. Bill Gibson filmed their runs down the right, which show them eddying out on river right upstream of the Black Rock. The September 1939 debris flow changed all that, creating a rapid with a higher velocity and greater drop. The rapid fascinated P.T. Reilly, who first saw the rapid in 1949. Reilly loved to photograph Lava Falls from John Riffey's light plane, flying low over the rapid. In so doing, Reilly documented the 1954, 1955, and 1963 debris flows in his aerial views, as well as capturing the widening out of the rapid by Colorado River floods, particularly the 1957 flood. Georgie White, interestingly enough, witnessed the 1954 debris flow as it occurred, describing it in her diary as a “big black lava flow.” She is one of the few people who have ever witnessed a Grand Canyon debris flow. The 1955 debris flow, combined with rearrangement of boulders by the 1957 flood, created most of the now-familiar features of the rapid, including the Ledge Hole and the V-Waves.

A hiker friend of Marston's photographed the rapid shortly after the 1963 debris flow. Once again, the river was highly constricted (by sixty percent), and low releases from the newly completed Glen Canyon Dam limited removal of its boulders until a 55,000 cfs dam release in May 1965. The December 1966 storm that caused Crystal Rapid to become so severe also created a small debris flow at Lava Falls Rapid, although it took a chance photograph from a Georgie White passenger to document it. John Cross, Jr. was the only boatman to notice the 1966 debris flow, noting that the deposition closed a left run. That changed after a Little Colorado River flood widened the rapid again in 1973. A generation of Grand Canyon guides became familiar with the rapid, which didn't change for 22 years, even during the 1983 flood. The March 1995 debris flow constricted the river once again, convincing that generation of boatmen that Lava Falls isn't an ancient, unchanging rapid after all. Following a little rearrangement of boulders courtesy of some dam releases, a reliable run left of the Ledge Hole became available at most water levels, and those who went right anyway risked getting caught in the Corner Pocket, a whirlpool just upstream of the Black Rock that became much more intense after 1995. At least one portage over the Black Rock to escape the Corner Pocket is now legendary in river-running history.
Since 1995, a number of streamflow floods from Prospect Canyon have thrown new boulders from the debris fan into the river. The left run, which was beautifully smooth just after the 1995 debris flow, is now pretty bony at most water levels, but people still run left and risk the wrath of Big Bertha or the Domer Rock, whichever name you prefer. Some people have flipped on the roostertail wave adjacent to the Ledge Hole; others have slipped into the Ledge Hole during the deceptive entry. Other boaters continue to run right, and unlucky ones like Brian Dierker end up in the Corner Pocket. One thing is for sure: Lava Falls will continue to change during the remainder of our river running careers. It is only a question of when the next debris flow is going to hit. Lava Falls is by far the most unstable rapid in Grand Canyon.

For more detailed information on Lava Falls Rapid, you may want to obtain the following publication:
Robert H. Webb and others, “Lava Falls Rapid in Grand Canyon: Effects of Late Holocene Debris Flows on the Colorado River,” us Geological Survey Professional Paper 1591, 1999.
This publication is available for about $15 from the following address:
usgs Information Services
Box 25286, Federal Center
Denver, co 80225–0286

Bob Webb and Peter Griffiths