Geology 17 (Landslides and Mass Wasting)

Earth and Space Sciences X

13 Dec 202170:03

EducationalLearning

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TLDRThe script discusses the geological processes and hazards of landslides and mass wasting - the movement of earth under gravity. It examines triggers like oversteepening, loss of vegetation, and earthquakes. Details are provided on classifications and velocities of movements like slides, flows, and avalanches. Monitoring methods are outlined to detect developing landslides, as well as mitigate risks that cause thousands of deaths annually, through mapping, sensors, lasers and radar.

Takeaways

😲 Landslides kill over 4,000 people per year and cause massive destruction
😃 Slopes consisting of barren rock, rubble, soil and vegetation are everywhere on Earth
👍🏻 Gravity is the main driving force behind mass wasting and landslides
🌧️ Water saturation greatly increases risk of landslides by adding weight to soil
⛰️ Oversteepened slopes from road cuts or stream erosion often fail and slide
🌳 Removing vegetation eliminates root anchors holding soil together
🌋 Earthquakes trigger thousands of dangerous landslides
🏔️ Fast deadly slides like rock avalanches and debris flows reach 100+ mph
🐌 Slow imperceptible soil creep tilts fences and trees over decades
📏 Monitoring with lasers, radar and satellites helps predict landslides

Q & A

What are landslides and how do they contribute to the death of mountains?
-Landslides are a geological hazard that involves the downslope movement of rock, regolith, and soil under the direct influence of gravity. They are a major process through which mountains 'die' by breaking down and transporting materials from higher elevations to lower areas.
How many people approximately die from landslides each year?
-Landslides kill over 4,000 people a year.
What are some examples of natural landscapes where slopes are common, and how do these slopes vary?
-Slopes are very common in various physical landscapes, including steep areas like young mountain ranges, moderate or gentle slopes such as those in the Great Plains of Russia, the United States, Brazil, or the central shield of Africa. Slopes can vary from long and gradual to short and abrupt.
What are talus and scree, and how do they differ?
-Talus and scree are types of loose, rocky material formed by weathering on slopes. Talus refers to cobble-sized materials or larger that have moved in a fall, while scree typically describes gravel-sized materials or smaller. The distinction often depends on the size of the materials and whether they have been involved in a rock fall.
What role does water play in landslides?
-Water adds weight to the soil, increasing the risk of landslides by adding mass (similar to a wet sponge being heavier than a dry one). It can cause soil and regolith to lose cohesion when saturated, acting as a lubricant that promotes sliding.
What are some triggers for landslides?
-Triggers for landslides include saturation of material with water, oversteepening of slopes, removal of anchoring vegetation, and ground vibration from earthquakes.
What is the difference between a rock slide and a debris slide?
-A rock slide involves blocks of bedrock breaking loose and sliding down a slope, whereas a debris slide involves unconsolidated material like soil and regolith sliding down. After the initial sliding, material can break up into a debris avalanche.
What is a lahar, and why is it considered extremely dangerous?
-A lahar is a debris flow composed mostly of volcanic materials that can occur during or after a volcanic eruption or even when a volcano is quiet. Lahars can be exceedingly deadly, burying towns and killing tens of thousands of people, as they do not require rain to initiate and move rapidly down slopes.
How can landslides be detected and monitored?
-Landslides can be detected and monitored through field mapping of ground deformation, displacement instruments, slope-movement sensors, pore pressure meters, and modern techniques like laser and radar surveys, photogrammetry, and satellite measurements.
What is creep in the context of landslides, and how does it manifest?
-Creep is the imperceptibly slow, gradual movement of soil and regolith downhill, aided by the alternate expansion and contraction of the surface material due to temperature changes. It can cause structures like fences and utility poles to tilt over time.

Outlines

00:00

🧗 Introduction to landslides and mass wasting

05:00

🏞 What is mass wasting and what causes it?

10:02

💧 The role of water in landslides

15:02

🔻 How oversteepening causes landslides

20:04

🌳 Vegetation removal triggering landslides

25:04

🌋 Earthquakes triggering landslides

30:06

🏔 Types of landslide material

35:08

💨 Rapid landslide types

40:10

🌊 More on debris flows

45:11

🌋 More on lahars

50:14

❄️ Snow avalanches

55:15

🛷 More on snow avalanches

00:16

🪨 Slumps and flows

05:17

🐌 The slowest landslide type - creep

🕵️‍♂️ Detecting and monitoring landslides

🌱 Ongoing landslide hazards

Mindmap

Keywords

💡mass wasting

Mass wasting refers to the downslope movement of rocks, soil and regolith under the influence of gravity. It is a key process in how mountains erode and eventually die over long timescales. The video examines different types of mass wasting like slides, flows and avalanches.

💡landslide

A landslide is a sudden event involving rapid downslope movement of rock and soil. Landslides are a major geological hazard that can destroy property and claim lives. The video analyzes triggers like earthquakes and oversteepened slopes that can cause devastating landslides.

💡angle of repose

The angle of repose refers to the steepest angle at which loose granular materials like sand or gravel can rest stably on a slope. Exceeding this angle due to human activities like road construction can trigger landslides.

💡debris flow

A debris flow is a dangerous type of rapid mass wasting where loose soil and rock flows swiftly downslope like a viscous fluid. Debris flows often occur in mountains during intense rainfall and can be highly destructive.

💡lahar

A lahar is a swiftly moving debris flow originating from a volcano, usually caused by melting snow and ice. Lahars can travel long distances along valleys and have been responsible for thousands of deaths near volcanoes.

💡creep

Creep is extremely slow, imperceptible downslope movement of soil and regolith, aided by freezing and thawing cycles. Creep can tilt fences, poles and other structures over long time periods.

💡slump

Slumping occurs when a mass of rock or soil moves downward as a single unit over a curved failure surface, not travelling very far. It results in visible ground disturbances like head scarps and rotated blocks of material.

💡mitigation

Mitigation refers to steps taken to reduce risks posed by landslides, like installing drainage pipes to remove water and prevent saturation of vulnerable slopes.

💡monitoring

Monitoring involves measuring ground deformation and slope movement over time to detect developing landslides. This is key for early warning systems to protect lives.

💡precipitation

Abundant precipitation as rainfall or snowmelt adds weight to slope material and aids mass wasting processes like debris flows and earthflows, making them more likely.

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Transcripts

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