View to the
west-southwest with Toroweap Point (North Rim) in the lower
right corner. A dirt road (broken black line) extends to the
Toroweap Overlook with Vulcans Throne (a volcanic cinder cone)
just above it. The Toroweap Fault enters from the right edge
(near the road) and continues leftward thru the front side of
Vulcans Throne and across the river through Prospect Canyon.
The far side of the fault has been down dropped some 600 feet.
This section of the Grand Canyon has seen a great
deal of volcanic activity in the last million years. Multiple
lava flows have cascaded into the canyon forming dams and
temporarily created lakes up to several hundred miles long.
Each time lava has blocked the channel, the Colorado River has
gone to work to re-excavate the canyon. Vulcans Throne has
been active as recently as 74,000 (+/- 4,000) years ago while
cinder cones have been active even more recently in Prospect
Prospect Canyon is of particular interest. It has
been filled several times with lava flows and is only just
starting to erode a new canyon down to the river. Also, these
lava flows sit right on the fault line, and each time the
fault moves, it shatters some of the old lava. The watershed
for the canyon extends some 20 miles further south, which
means a large amount of water can come down the canyon during
a flash flood. The combination of large amounts of water,
shattered rock, and a steep drop to the bottom of the Grand
Canyon allows large volumes of debris to pile up where it
meets the Colorado River. The result is Lava Falls Rapid.
View to the
west-southwest with Vulcans Throne in the lower right corner
and Prospect Creek/Canyon entering from the left edge. Lava
Falls Rapid is near the bottom edge where Prospect Creek joins
the Colorado. River mile 184 is in the distance where the
river is furthest to the right.
Most of the Prospect Canyon debris fan was
deposited in a huge debris flow about 3,000 years ago. This
river blockage is responsible for Lava Falls Rapid and also
backed up the Colorado River for at least 20 miles. River
gradient is still relatively low for 20 miles upstream.
Prior to 1939 it was debatable whether Lava Falls
or Hance Rapid was the "baddest" on the river. Then another
debris flow (estimated at 35,000 cu. ft. per sec.) down
Prospect added to the debris fan and settled the issue. In
1966 a major debris flow down Crystal Creek created Crystal
Rapid and once again there is a "baddest" debate. Prospect
Canyon had another debris flow on March 6, 1995 that
constricted Lava Falls Rapid again, but not enough to settle
the issue. As to which rapid will become the worst - stay
tuned. It might happen just as you start a future raft trip.
Near the center of the picture, the river bends
slightly to the left before cutting back to the right. Before
the series of lava flows that started about 1.2 million years
ago, the river took a straighter path through this section.
Then black basaltic lava flows from the north (right side of
the river) filled in the old inner gorge and forced the river
up against the left wall of the canyon. The river subsequently
eroded straight down in this new deflected path. If you are
rafting the river, the right side of the canyon reveals a
cross section of the former, filled-in channel.
river miles 168 to 176
to river miles 184 to 192
the Index Page for the Grand Canyon Tour
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