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Slope basics -
measurement, stability, variables
Types of mass wasting –
slumps, slides, falls, creep
Hazards – susceptible locations,
Human impacts and hazards
Like other gravity physics problems, slope is stable if forces are equal
Mass movement or wasting occurs if stress overcomes friction, and slope fails – gravity always wins!
Major factors: The overall strength of the material determines how much stress it can takeGeologic bedding , joints or other features can alter strengthWater greatly reduces friction failureEvents can reduce strength suddenly
Creep – slow, most active at the surface, usually in soft stuff like soil
Rockfall– material free falls at failure, motion is rapid and violent
Slumps – material moves downslope accompanied by rotation
Slides – material moves as cohesive unit along a clearly define surface
Flows – material moves chaotically and in a disorganized fashion
Avalanches or debris flow –involve a wide range of material
Areas of US most susceptible to failure include combinations of more than one of the risk factors
Tectonicslandscapemotion
Climate & ariditySeasonalityGeology
Mitigation involves both avoiding bad practices and adding good ones, increasing slope stability
Building practices can GREATLY affect risk of failure
Geology: hills, bluffs, glacial valleysO Mostly flatO Not rockysoft, weak materialsClimate: Wet and coldO Not arid or flashy
Result: lots of risk in valleys and soft hillslopesGradual >>> sudden – example lots of creep, occasional slumps
Limestone / shaleSlide and fall potential
Minnesota has specific risks & locations
Building do’s
Avoid the most failure-prone areas
Build retention structures into slope
Predict water impacts and plan drainage
Mechanical strengtheningVegetation tends to stabilize slopes
Building don’t’sAvoid slope oversteepeningReduce the load on the slopePrevent natural & artificial water hazards
Don’t build in the wrong place!
Glacier formula: accumulation > melting
Eventually a huge icepack will push down and begin to move via gravity – an ‘ice river’
1] Mountainglaciers are more common, smaller than
2] Continentalglaciers
Large continental glaciers are enormously heavy, with lobes and great climatic influence
… and 75 % of our fresh water
1] The Giant Bulldozer – scrapes with enormous force. Removes unbelievable tonnage of rock, sculpting huge valleys, holes and features
2] The Giant Dump Truck - drops glacial drift sediment load as till, big round or long mounds left by receding ice, or outwash
Some of the rocky debris left by receding ice is familiar as out of place erratics
Some of the best geology terminology: ‘kames’, ‘eskers’, and ‘jöhkulhlaup’
Easy ones: kettle depressions caused by ice blocks and moraine features piled up by glacial deposits
Moves around a fair amount of sediment in the sand and silt ranges
Silt sized particles move great distances, form loess depositsCan be cold or warm + dry
ripplesdunes
Distribution of dry regions dominated by wind processes
Occur in rain shadow of mountains
wind wet dry
Warm latitudes dominate; but cold deserts (tundra) at poles
Regular orbital cycles have major influence on sun’s warmingAtmosphere has huge influence on keeping the warmth [greenhouse effect]
Ice sheets and desertsgrow & shrink in responseto global heat
Distance and angle from sun is directly linked to climate & ice ages, warm spells