Lava Falls Rapid in Grand Canyon: Effects of Late Holocene debris flows on the Colorado River

Webb, Robert H.; Melis, Theodore S.; Griffiths, Peter G.; Elliott, John G.; Cerling, Thure E.; Poreda, Robert J.; Wise, Thomas W.; Pizzuto, J. E.

doi:10.3133/pp1591

Cited by 42 publications

(28 citation statements)

References 43 publications

(83 reference statements)

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“…Most debris fl ows occur in summer (Webb et al, 1989(Webb et al, , 1999(Webb et al, , 2000, when convective thunderstorms yield intense rainfall (Hereford and Webb, 1992;Hereford et al, 2002). Webb et al (2000) report no relation between debrisfl ow occurrence in Grand Canyon and total seasonal precipitation; instead, they hypothesize that debris-fl ow occurrence is better related to wet periods where antecedent soil moisture can accumulate over short (~1-week) periods.…”

Section: Infl Uence Of Rainfall Distribution and Intensitymentioning

confidence: 94%

“…2D). Debris fl ows with lower clay contents (~1% or less), such as those that occur at Prospect Canyon in Grand Canyon (Webb et al, 1999), fl ow short distances before losing too much mass to sustain boulder transport. Certain units of fi ne-grained bedrock fail readily, either producing debris fl ows directly or storing sediment to colluvial deposits, which can fail later.…”

Section: Infl Uence Of Sediment Sourcesmentioning

confidence: 99%

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Holocene debris flows on the Colorado Plateau: The influence of clay mineralogy and chemistry

Webb

Griffiths

Rudd

2008

Geological Society of America Bulletin

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Holocene debris fl ows do not occur uniformly on the Colorado Plateau province of North America. Debris fl ows occur in specifi c areas of the plateau, resulting in general from the combination of steep topography, intense convective precipitation, abundant poorly sorted material not stabilized by vegetation, and the exposure of certain fi ne-grained bedrock units in cliffs or in colluvium beneath those cliffs. In Grand and Cataract Canyons, fi ne-grained bedrock that produces debris fl ows contains primarily single-layer claysnotably illite and kaolinite-and has low multilayer clay content. This clay-mineral suite also occurs in the colluvium that produces debris fl ows as well as in debris-fl ow deposits, although unconsolidated deposits have less illite than the source bedrock. We investigate the relation between the clay mineralogy and major-cation chemistry of fi ne-grained bedrock units and the occurrence of debris fl ows on the entire Colorado Plateau. We determined that 85 mapped fi ne-grained bedrock units potentially could produce debris fl ows, and we analyzed clay mineralogy and majorcation concentration of 52 of the most widely distributed units, particularly those exposed in steep topography. Fine-grained bedrock units that produce debris fl ows contained an average of 71% kaolinite and illite and 5% montmorillonite and have a higher concentration of potassium and magnesium than nonproducing units, which have an average of 51% montmorillonite and a higher concentration of sodium. We used multivariate statistics to discriminate fi ne-grained bedrock units with the potential to produce debris fl ows, and we used digital-elevation models and mapped distribution of debrisfl ow producing units to derive a map that predicts potential occurrence of Holocene debris fl ows on the Colorado Plateau.

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Section: Infl Uence Of Rainfall Distribution and Intensitymentioning

confidence: 94%

Section: Infl Uence Of Sediment Sourcesmentioning

confidence: 99%

Holocene debris flows on the Colorado Plateau: The influence of clay mineralogy and chemistry

Webb

Griffiths

Rudd

2008

Geological Society of America Bulletin

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“…Many researchers have described the rapids that dominate the river corridor of Grand Canyon [ Leopold , 1969; Howard and Dolan , 1981; Kieffer , 1987]. Other researchers have more fully documented the role of debris flows in the creation and maintenance of debris fans and rapids [ Cooley et al , 1977; Webb , 1996; Webb et al , 1989, 1999a, 2003; Melis et al , 1994]. Given their episodic nature, debris flows result in large modifications to debris fans and associated rapids over very short time periods, in most cases minutes to hours [ Webb et al , 1988, 1999a].…”

Section: Debris Flows and The Colorado River In Grand Canyonmentioning

confidence: 99%

“…Other researchers have more fully documented the role of debris flows in the creation and maintenance of debris fans and rapids [ Cooley et al , 1977; Webb , 1996; Webb et al , 1989, 1999a, 2003; Melis et al , 1994]. Given their episodic nature, debris flows result in large modifications to debris fans and associated rapids over very short time periods, in most cases minutes to hours [ Webb et al , 1988, 1999a]. River reworking of newly aggraded debris fans, which was extensive on the unregulated river [ Melis , 1997], occurs on a limited basis on the regulated Colorado, typically during maximum power plant releases or intentional flood releases from Glen Canyon Dam [ Webb et al , 1999b].…”

Section: Debris Flows and The Colorado River In Grand Canyonmentioning

confidence: 99%

“…Despite reworking, the riverbed has risen at tributary confluences during the Holocene [ Webb et al , 1999a] and historically [ Melis et al , 1994; Webb et al , 1999b] owing to debris flow deposition. The large boulders deposited in the river by debris flows form the core of rapids that modify the longitudinal profile and locally control the geomorphic framework of the present‐day Colorado River in Grand Canyon (Figure 3) [ Webb , 1996].…”

Section: Introductionmentioning

confidence: 99%

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Frequency and initiation of debris flows in Grand Canyon, Arizona

2004

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Debris flows from 740 tributaries transport sediment into the Colorado River in Grand Canyon, Arizona, creating rapids that control its longitudinal profile. Debris flows mostly occur when runoff triggers failures in colluvium by a process termed “the fire hose effect.” Debris flows originate from a limited number of geologic strata, almost exclusively shales or other clay‐rich, fine‐grained formations. Observations from 1984 through 2003 provide a 20 year record of all debris flows that reached the Colorado River in Grand Canyon, and repeat photography provides a 100 year record of debris flows from 147 tributaries. Observed frequencies are 5.1 events/year from 1984 to 2003, and historic frequencies are 5.0 events/year from 1890 to 1983. Logistic regression is used to model historic frequencies based on drainage basin parameters observed to control debris flow initiation and transport. From 5 to 7 of the 16 parameters evaluated are statistically significant, including drainage area, basin relief, and the height of and gradient below debris flow source areas, variables which reflect transport distance and potential energy. The aspect of the river channel, which at least partially reflects storm movement within the canyon, is also significant. Model results are used to calculate the probability of debris flow occurrence at the river over a century for all 740 tributaries. Owing to the variability of underlying geomorphic controls, the distribution of this probability is not uniform among tributaries of the Colorado River in Grand Canyon.

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A fault runs through it: Modeling the influence of rock strength and grain-size distribution in a fault-damaged landscape

Roy

Tucker

Koons

et al. 2016

J. Geophys. Res. Earth Surf.

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We explore two ways in which the mechanical properties of rock potentially influence fluvial incision and sediment transport within a watershed: rock erodibility is inversely proportional to rock cohesion, and fracture spacing influences the initial grain sizes produced upon erosion. Fault‐weakened zones show these effects well because of the sharp strength gradients associated with localized shear abrasion. A natural example of fault erosion is used to motivate our calibration of a generalized landscape evolution model. Numerical experiments are used to study the sensitivity of river erosion and transport processes to variable degrees of rock weakening. In the experiments, rapid erosion and transport of fault gouge steers surface runoff, causing high‐order channels to become confined within the structure of weak zones when the relative degree of rock weakening exceeds 1 order of magnitude. Erosion of adjacent, intact bedrock produces relatively coarser grained gravels that accumulate in the low relief of the eroded weak zone. The thickness and residence time of sediments stored there depends on the relief of the valley, which in these models depends on the degree of rock weakening. The frequency with which the weak zone is armored by bed load increases with greater weakening, causing the bed load to control local channel slope. Conversely, small tributaries feeding into the weak zone are predominantly detachment limited. Our results indicate that mechanical heterogeneity can exert strong controls on rates and patterns of erosion and should be considered in future landscape evolution studies to better understand the role of heterogeneity in structuring landscapes.

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Lava Falls Rapid in Grand Canyon: Effects of Late Holocene debris flows on the Colorado River

Cited by 42 publications

References 43 publications

Holocene debris flows on the Colorado Plateau: The influence of clay mineralogy and chemistry

Holocene debris flows on the Colorado Plateau: The influence of clay mineralogy and chemistry

Frequency and initiation of debris flows in Grand Canyon, Arizona

A fault runs through it: Modeling the influence of rock strength and grain-size distribution in a fault-damaged landscape

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