Presentation on theme: "Mass Wasting & Soil Survey. Objectives Show some case studies of how soil surveys handle landslides. – Guam – North Dakota – Alabama – California Discussion:"— Presentation transcript:
Objectives Show some case studies of how soil surveys handle landslides. – Guam – North Dakota – Alabama – California Discussion: are we doing enough? – Are we alerting our users to conditions and potentials for slope failures?
Island of Guam Affected by rotational landslides, in certain soils. Just looking at the DEM, can you guess where they occur?
Eocene, Oligocene & Miocene; tuff, tuff breccia, tuffaceous sandstone/shale Pliocene & Pleistocene; Reef complex, reef detritus SSURGO soils of Guam Grouped by parent material (mostly)
Typical slides in soft, deeply weathered volcanic saprolite Anthropic grasslands are incapable of stabilizing this material: tectonic uplift; deeply dissected; 80-100” rainfall; seasonally distributed All pictures by Bob Gavenda, SS in Guam
Rotational Slides provide parent material for Togcha soils in footslope positions Akina (residuum in saprolite) Togcha (“slope alluvium” in SS; what should we call it?) Note: taxonomic classifications shown are out of date. The soil survey does not clearly address the issue of rotational slides.
Slides and soil survey in North Dakota McKenzie county Barnes county
McKenzie county, ND Lots of badlands – any slides? Little Missouri R
IFSAR hillshade added… Do the slides stand out more?
116F—Kremlin-Cabbart loams, slumped, 9 to 40 percent slopes Setting: Kremlin soils occur on footslopes. Cabbart soils occur on summits and shoulders. This map unit occurs on ridges that are slumped in badlands. Map Unit Composition (percent) Named Components Kremlin and similar soils: 15 to 45 percent Cabbart and similar soils: 15 to 50 percent Average Component Composition Cabbart: 29 percent Kremlin: 19 percent Boxwell: 17 percent Scairt: 14 percent Lonna: 13 percent Badland, outcrop: 5 percent Fleak: 3 percent From the soil survey manuscript (Aziz et al, 2006)
Valley City, ND Barnes county. Sheyenne R., I-94 at Valley City. Where are the slides?
Summary and Discussion Mass wasting is handled in various ways in county soil surveys: – Components; e.g., badlands – Map unit name; e.g. slumped Failure zones are implicitly identified in county soil surveys: – Contrasting components within map units – Boundaries between map units Discussion: can we do better? – i.e., clearly alert users to landslide activity and hazards, both spatially (maps) and in attributes / interpretations.