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

Abstract

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.

Discrimination of debris flow in narrow-steep type and wide-gentle type gullies in Wenchuan meizoseismal area

“…The proportion of rock blocks is large, while the total amount of less than 200 mm blocks is also relatively large, which is easy to initiate. Webb et al (2008) investigated the relationship between the clay mineralogy and major-cation chemistry of fine-grained bedrock units and the occurrence of debris flows on the entire Colorado Plateau, finding that the debris flow producers are uniformly low in montmorillonite (5%) and high in illite and kaolinite (71%); conversely, fine-grained bedrock that does not produce debris flows has lower illite and kaolinite (25%) and higher montmorillonite (51%) content. Analysis of the clay mineral composition of the deposit source in the meizoseismal area by X-ray diffraction experiments revealed that it is mainly composed of three clay minerals (Figure 7): illite, chlorite, and illitemontmorillonite mixed-layer, with an average content of 45.6%, 38.8%, and 15.6% respectively.…”

Environmental variation shapes genetic variation in Bouteloua gracilis: Implications for restoration management of natural populations and cultivated varieties in the southwestern United States

“…Further strengthening the distinction between the boundary and the interior of the Colorado Plateau is the distribution of cytotypes (Table 1) While distinct climate patterns, such as divergence in MAP (National Research Council, 2007;PRISM Climate Group, 2004) and MAT (PRISM Climate group, 2004), drive the differentiation of ecosystems on the Colorado Plateau, with drylands dominant in the interior and pinyon-juniper and montane forests dominant at and above the boundary (National Park Service, 2016), other biotic and abiotic factors may further shape the genetic variation observed in blue grama between these two regions. For example, the interior and the boundary regions of the Colorado Plateau also have markedly different topologies, soils, fire return intervals, and drought intensity patterns (Fule, Covington, & Moore, 1997;Miller & Tausch, 2001;Reynolds, Belnap, Reheis, Lamothe, & Luiszer, 2001;The National Drought Mitigation Center, 2017;Webb, Griffiths, & Rudd, 2007).…”

Early Pleistocene Debris-Flow Deposits in the Upper Jinsha River, Sw China and their Paleoenvironmental Implications

“…According to previous studies [1][2][3][4][5][6], we have known that there occur many Quaternary debris-flow deposits in the southeastern (SE) marginal area of the Tibetan Plateau (TP), especially in valleys of the upper reach of the Jinsha River and that they can provide rich information for geomorphic evolution, tectonic movement or climate change and others. In valleys of the upper reach of the Jinsha River, Zhang [7] identified one planation surface, two erosion surfaces and seven levels of alluvial terraces.…”