Terrain Management With Shelly Higman Flashcards
What is a landslide? How are they classified?
Any downward movement of rock, categorized by material type and type of movement.
What is the most common slide?
A debris slide: fairly shallow, 1-2 m depth. Deposits debris as terrain flattens.
What is a the name for a bigger slide where the ground rotates as mass slumps downward?
Rotational slump: Classic features include failure plane, head, foot, toe, scarp, transverse faulting, transverse ridges (conversion of slump to flow).
What is a common cause of failure?
Plugged culvert
What is a common coastal slide triggered by heavy precipitation events?
Debris flow: no internal structure. Quick and violent with a long range. Gullies are at increased risk.
Gully definition
Defined channel with stream with at least 1 100 m reach
Fan to apex gradient of 25% or more
What soil instability factor describes slow movement of soil?
Soil creep: has not yet failed but can lead to future failure
What are the mechanisms that govern the safety factor system?
Driving forces
Resisting forces
Describe driving factors
Inherent factors: soil composition and structure
External factors: undercutting and seismic force
Explain resisting forces
Shear strength
Inherent factors: strong or weak soil, soil types
External: weathering, pore water pressure
What is the strongest material on the coast?
Till: sediment size from clay to boulders, compacted by years of ice, Unsprted
Another strong soil type?
Colluvial: Gravity deposition, sharp edges, Unsorted
Next strongest after collivial?
Glacio fluvial
Worst soil type for stability
Glacio- lacustrine
Contributing factors
Elevation: snow and rain on snow are frequent contributors
Hydrologic region: wet or dry
Slope geometry: gradient (convex catches water), shape (the smoother the worse)
What is a natural event that can cause lateral pressure?
Frost heaving
What are some important field indicators of landslides?
Recent landslide scars or revegetated scars
Jack strawed trees
Debris piled on lower slopes
Soil and rocks piled on upside of trees
Pistol butt trees
Tension fractures
Standing water on steep slopes, or bulges in a slope
High textured materials, especially above 30 %
What are some sure wet site indicators?
Indian hellebore, Devils club, maidenhair Fern, skunk cabbage.
How Can you identify old failures by landform?
Look for track and change in vegetation age
What is the most important thing for a forester to know with respect to terrain stability?
Indicators of slope instability
