Chapter 08,9

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!

2011:it rained 26 cm in less than 24 hrs

Many, many missing

Sun & climateGlacier typesGlacial processesDesert processesHuman inpact

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