View is to the northwest along cobble-rich debris flow near
Spring Lake. The High Line canal, which was partly filled
with debris, extends across the middle of the photo.
Click here for larger image.
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By Christopher B. DuRoss
and Greg N. McDonald
Intense rainfall in the afternoon and evening of July 26th,
2004, triggered two fire-related debris flows south of Provo,
near Spring Lake and Santaquin, Utah. Mud-, cobble-, and boulder-rich
sediment discharged from two drainages on the northwest flank
of Dry Mountain, and was deposited on alluvial fans north
of the range-front. The debris originated from drainage areas
burned by the human-caused 8,000-acre Mollie wildfire of 2001.
The fire-related debris flows were in the same general location
as the two northernmost flows of September
12th, 2002; however, the July 2004 flows were smaller
and did not travel as far north as the 2002 flows (see maps
below). No damage to residential homes or property was reported.
Conversely, the September 2002 flows resulted in significant
damage to a subdivision due to a large volume of debris that
originated from a drainage farther to the south. No debris
flows were generated from that drainage in the July 2004 storm.
The larger debris flow is located southwest of Spring Lake
and traveled to the northwest, filling part of the High Line
irrigation canal with cobbles and silt. The debris was quickly
excavated to prevent overflow and flooding of the canal.
The thickness of new material in the 2004 deposit could
not be determined as an unknown amount of the September 2002
debris was incorporated into the flow.
About a mile east of Santaquin, a smaller debris flow traveled
to the northwest into a storm-water catchment basin. The deposit
is approximately 9 to 12 inches thick.
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