ESS 17-Mass Waiting & Sink Holes

What mechanisms can cause slopes to fail?

+Down-slope movement of rock +Soil or sand due to the force of gravity Mass wasting is a form of erosion; all mountains fall eventually.

Translational Slide

Slip Parallel to slope, may move as coherent mass or break up into debris flow. No backwards rotation...movement is down-slope but forward. Faster and farther than slumps.

Soil Creep

Slow creep of soil overtime, slow soil, weak rock.

Rotational Slide

Slump Most common slide, slide along a curved plane. Homogeneous, cohesive, soft materials. Unconsolidated materials, weak rocks (mud-stone, shale).

Potential Energy

Stored energy

What is Karst (limestone) topography, and how does this type of terrain result in sinkholes?

This type of terrain results in sinkholes because impermeable overburden contains clay that sits atop limestone, causing the soil cavities to grow large. They then become unstable and collapse.

Predict how human land-use practices (like oil groundwater extraction) might impact subsidence

Will result in the ground lowering, significantly over time.

Compare and Contrast Cover-Subsidence to Cover-Collapse Sink Holes

+Cover-Subsidence DOWNWARD MOVEMENT of Earth to fill a void, can be natural process of human-induced. Generally, years in the making but maybe a SUDDEN collapse. Mainly composed of LIMESTONE. +Cover-Collapse Where IMPERMEABLE overburden contains CLAY and sits ATOP immediate limestone, soil cavities grow large, become unstable and collapse suddenly into STEEP-SIDED sinkhole-most dangerous.

What types of sinkhole is the most dangerous and why?

Cover-Collapse sinkholes are the most dangerous because the soil cavity grows large and becomes unstable causing it to collapse suddenly into a step-sided sinkhole. For example: Man in Florida fell through his bedroom floor and died due to this type of sinkhole.

Kinetic Energy

Energy that is in motion

Rockfall

Free-falling; fast rock; triggered by freezing water or ground shaking. Cliffs w/ nearby vertical fractures or weaknesses.

Given a slide-prone area, determine proper techniques to prevent a landslide... (Hint: 4 Rs)

Revegetation Regrading Reducing subsurface water Preventing undercutting

Predict How far may a rockfall "run out" from a base of a cliff given its mass and height of a fall?

The heavier the rock, the more it will run out.

Mudflow

Very fine-grained (clay) particles. Doesn't need a large incline due to size particles. Harden in place, destroy everything in their place.

How can water change the load and weaken the shear strength of a slide-prone area?

Water increases driving force and decreases resisting force.

Debris Flow

Water, laden masses of mud rock, other debris move down-slope via force of gravity. Often happen on steep slopes after heavy rains.