Help
Options
Didn't know it?
click below
click below
Knew it?
click below
click below
Don't Know
Remaining cards (0)
Know
retry
shuffle
restart
0:00
Embed Code - If you would like this activity on your web page, copy the script below and paste it into your web page.
Normal Size Small Size show me how
Normal Size Small Size show me how
Earth 2
lectures 13
| Question | Answer |
|---|---|
| Once material is broken down by weathering continued | we can't change gravity so mass movements must be via a decrease in friction |
| Rock Falls | Rocks breaking from larger mass (like a mountain) and falls down slope. cracks, joints, faults in rocks allow the separation of the rock from the bedrock, eliminating friction |
| Slides | Coherent mass of material moves over the surface |
| Flows | material moves as a fluid from high to low. |
| Angle of repose | For dry, loose material (sand, gravel, boulders) the angle of repose is 30 degrees. Clays are different, electrically charged, "Playing card" shape of clay minerals and polarity of water |
| Tilted bedding | increasing the tilt doesn't change gravity, but it does change the resultant downward force |
| Frank slide | 3, April 1903. 4:10 am. Over steep cliff, tensional cracking from folding, less competent rock underneath made cliff unstable, possible frost wedging |
| Cliff fall | continuous wave action flexes the rock and weakens it over time, abrasion at the base can also weaken the rock, there also may be jointing due to previous tectonic activity |
| Frank slide cliff fall | continuous wave action undercuts the cliff face, creating greater instability. Relentless rain |
| Slump-eruption of Mount St. Helens | In Washington state, was preceded by the largest mass movement in current history. Increasing magma over steepened the northern flank of the volcano, the slump released the weight holding the volcanic pressures in check, so eruption. Cascading hazards |
| Slump | Saturated soil increases hydrostatic pressure, water pressure is in all direction, close to the cliff (or scarp), there is no pushing back, decreasing frictional force. Slump is a rotational deformation |
| Vajont Landslide | 1957-1960. Worlds tallest dam at the time, still one of the tallest. Filling the reservoir raised groundwater levels saturating a clay layer. Wet clay, low friction. Mountainside slid into reservoir, tsunami 250m high 200 deaths |
| Vajont landslide the geology of the problem | The monocline in limestone allowed the very deep and narrow gorge to be cut; ideal for a tall dam. Early signs of trouble caused some testing of water level and land sliding. engineers thought they could control a mountain |
| Capillary Action | Adhesive properties of water makes it climb up from grain to grain. Attraction to other particles is greater than gravity. Cohesive properties of water means it will pull water up with it |
| Capillary action and rocks | The clay under the limestone absorbed the water and became slippery (lower friction)so no change in slope, but a decrease in friction allowed the slab of rock to slide down the bedding plane |
| Alta, Norway landslide | 3 June 2020, Area sitting mostly on clay that may have been saturated, decreasing friction (quick clay like liquefaction), 8 houses lost, no people |
| Debris flow | water mixes with sediment and becomes a dense slurry, because it is so dense, it can pick up more and bigger stuff to transport. They can travel for kilometers, to places where there was no sign of bad weather |
| Mud slide | Like a debris flow but without all of the debris. Near Edworthy park. glacial till on top of sandstone |
| Avalanche | Snow will not follow the 30 degree angle of repose rule due to polar nature and melting/refreezing activities. Over steepened slopes are common giving way to avalanches. Closing roads and controlled avalanches are in repertoire to keep people safe |
| Know the risks: geological causes for mass movements | weak or sensitive materials, weathered materials, sheared, jointed, or fissured materials. Adversely oriented discontinuity (bedding, schistosity, fault, unconformity, contact), contrast in permeability and or stiffness of materials |
| Know the risks: Morphological (shape of the land) causes | Tectonic or volcanic uplift, glacial rebound, Fluvial, wave, or glacial erosion of slope toe or lateral margins. Subterranean erosion (solution, piping). Vegetation removal (by fire or drought). Thawing, freeze and thaw, shrink and swell weathering |
| Know the risks: Human Causes | Excavation of slope or its toe, loading of slope or its crest, drawdown (of reservoirs), deforestation, irrigation, mining, artificial vibration, water leakage from utilities |
| Engineering solutions | Understand the physics, understand the geology, model scenarios, engineer solutions |
| Modeling and simulations for lahars | Modeling is DETERMINISTIC. The parameters are all set. There are different case scenarios that are dependent on initial parameters. These are predictions of what will happen |
| Monitoring for ground motions | monitoring at Turtle mountain. Ground based interferometric synthetic aperture radar, constantly sends out signals, measures the return time, analyzes for mm-scale movement, passing a certain threshold triggers an alert |
| Monitoring | sensors for observing ground motions, tiltmeters for change in inclination. Piezometers to measure groundwater level and groundwater pressure. Data are continually collected and analyzed. Surpassing threshold triggers alert |
Created by:
user-1996284