LA L2: Landslide Causes and Triggers Flashcards

Question

Describe how water increases weathering of rocks.

Answer 1

Water increases the weathering of rocks when it flows into even the narrowest of rock fractures. When water goes through its freeze/thaw cycles, it can expand in volume by 9%. This volume change is a very powerful force that can wedge apart rocks, often causing them to fall from steep slopes in mountains and canyons.

Answer 2

Water in some pore spaces binds particles. Water between all particles keeps them apart and allows them to flow.

Answer 3

water affecting erosion rates, interacting with geologic materials, its affect on pore pressure

Answer 4

Storm systems that produce intense rainfall for periods as short as several hours or have a more moderate intensity lasting several days

Answer 5

more than 10 000 landslides. more than 200 deaths

Answer 6

In December 1999, heavy rainfall triggered thousands of debris flows along the northern coast of Venezuela. The death toll was estimated at 30,000 people. Heavy rainfall triggered thousands of debris flows and caused numerous flash floods in a 300-kilometer long area of the north coast of Venezuela. Rainfall amounts of 300 to 480 mm over the towns of Maiquetia and La Guaira on the coast north of Caracas, Venezuela.

Answer 7

A local, rainfall-triggered landslide occurred on January 19, 2005 in North Vancouver. During this rain event, the Coquitlam reservoir level increased by 557 mm between January 17 to 22. After 48 hours of heavy rain from tropical storm Kulap, a debris avalanche swept down an 80 meter slope in a residential neighborhood, destroying two houses, killing a woman, and prompting the Premier to declare a state of emergency.

Answer 8

its steeper slopes, but it also receives approximately three times more rainfall than what is reported at Vancouver International Airport because of its proximity to the North Shore mountains

Answer 9

proximity to the North Shore mountains

Answer 10

Heavy and prolonged rainfall can increase groundwater levels as a result of deep infiltration of abundant water. An elevated groundwater table tends to trigger more deep-seated and slower moving landslides such as slumps versus shallower, more fluid, and faster moving (and more dangerous) flows.

Answer 11

1995 and 2005 La Conchita landslides in southern California

Answer 12

accelerated erosion and frequent mud or debris flows triggered by intense rainfalls. Volcanic eruptions have directly triggered some of the largest historic landslides.

Answer 13

partially buried and destroyed by lahars

Answer 14

Located in the Andes mountains of South America, Nevado del Ruiz is the northernmost and highest Colombian volcano with historical activity.

Answer 15

might have been averted if government authorities had heeded warning. Colombian scientists monitoring the volcano had cautioned town leaders of Armero about the increased volcanic activity and even radioed urgent messages on the night of the eruption. But no systemic efforts were made to evacuate the town of 28 000. Authorities likely thought town was out of harm's way.

Answer 16

28 000 people. 45 miles from crater.

Answer 17

two and a half hours after the start of the eruption, a lahar buried Armero. The explosive eruption had rapidly melted much of the volcano's snow-covered glacier, sending water surging down canyons, picking up soil, volcanic ash, and red-hot rock as it went. More than three-quarters of the town's citizens perished.

Answer 18

Lahar traveled 100 km and left behind a wake of destruction: more than 23,000 people killed, about 5,000 injured, and more than 5,000 homes destroyed along the Chinchina, Guali, and Lagunillas Rivers.

Answer 19

a massive 2.8km^3 rockslide that was triggered by ongoing volcanic activity.

Answer 20

The rockslide descended and traveled 22 km down the valley.

Answer 21

The rapid melting of snow and ice from the eruption induced mud flows which surged down several valleys destroying almost everything in its path.

Answer 22

At 8:32 am a 5.1 earthquake shook loose the north flank of Mount St. Helens, resulting in the largest known landslide in historic time. Removal of more than half a cubic mile of material released pressure and triggered a devastating lateral blast and ash-laden (vertical) eruptive column.

Answer 23

Erupted often between 1980 and 1986. An explosive eruption sent pumice and ash 14 km into air, and resulted in a lahar flowing from crater into the North Fork Toutle River valley. Part of the lahar entered Spirit Lake (lower left corner) but most of the flow went west down the Toutle River, eventually reaching the Cowlitz River, 80 kms downstream.

Answer 24

Small magnitude earthquakes (M<4.0) generate falls over less than 10km^2 in area, while large magnitude earthquakes (M>6.0) can generate avalanches affecting areas 3 magnitudes larger. Liquefaction can easily be generated by smaller earthquakes.

Answer 25

thousands of landslides

Answer 26

by dislodging loose resting on steep slopes. Larger scale: seismic loads destabilize slopes by inducing shear stresses thereby weakening the internal structure of the slope material. (Alaska, 1964, when 56% of total cost of damage of M9.2 earthquake was caused by quake-triggered landslides.

Answer 27

The largest landslide in Anchorage was triggered by the M 9.2 Good Friday Earthquake in 1964, caused substantial damage to numerous homes in the Turnagain-By-The-Sea subdivision.

Answer 28

The earthquake-triggered landslide in El Salvador on 13 January 2001 killed 585 people. The earthquake magnitude was M 7.7.

Answer 29

A slope stability analysis of the Alaska earthquake-triggered landslide shows that the Factor of Safety decreased sharply due to both an increase in the shear stress and a decrease in the shear strength due to the effects of the earthquake.

Answer 30

1. Excavation of a slope at its toe (point at which lowest part of a slope intersects with natural ground line) 2. Loading of a slope at its crest. 3. Deforestation for construction and development (including clear-cut logging on slopes) 4. Irrigation 5. Mining 6. Water leakage from utilities 7. Artificial vibration (Blasting and the movement of heavy equipment during construction and mining can act as triggers for landslides.)

Answer 31

excavation of a slope at its toe, loading of a slope at its crest

Answer 32

to increase the size of a lot by extending its backyard.

Answer 33

Blasting through the base of a slope and creating near-vertical cliffs.

Answer 34

Bedrock has a higher shear strength than unconsolidated sediment; however, bedrock still must be evaluated for failure potential as it can be fractured and/or faulted, yielding a lower shear strength.

Answer 35

You will see that the weaker fracture planes in the cliff face that are likely to accommodate motion, slope toward the highway and resemble daylighted bedding

Answer 36

2013 Uttarakhand, India. Flood driven. 5700 deaths.

Answer 37

the material that UBC is built upon is composed of unconsolidated sands and silts. Wave action easily erodes and undermines the base of the cliffs that support the area where UBC sits.

Answer 38

during the last glaciation (Fraser Glaciation).

Answer 39

~23,000; 65; ~12,000; 0 - 5

Answer 40

They have been overridden and compacted by subsequent glacial advances.

Answer 41

Two berms (artificial beaches) have been constructed. Cliffs behind Museum of Anthropology were cut back to decrease shear stress. Vegetation was also planted to increase shear strength in those slopes.

Answer 42

Curtail coastal erosion and allow material from previous slides, large or small, to accumulate at the base of the cliffs until a stable configuration can be achieved. Berms effectively widen the natural beach, preventing waves from reaching the base of the cliffs.

Answer 43

In 1974, a berm composed of sand, gravel, and cobbles overlain by gravel found in natural deposits was constructed for 750 000. However, the ber However, the berm was breached by waves by late Fall 1975. The berm material was eventually transported ~2 km eastward to Spanish Banks by longshore drift by the spring of 1976. In the spring of 1982, a new berm was completed at a cost of $1.2 million (figure below). This berm consisted of well-sorted cobbles that allowed the energy from the crashing waves to dissipate instead of eroding the finer-grained material eastward. A series of groins (a structure made of concrete, rocks, or wood usually built to preserve the sediments in a beach) made of large boulders were constructed perpendicular to the beachfront in order to prevent the berm material and finer sands from being transported to Spanish Banks by longshore drift. These structures are still visible on the beaches.

Answer 44

1982 spring. $1.2 million

Answer 45

The cliffs were cut to a more gradual slope to decrease shear stress. Fences were built to prevent people from treading onto unstable cliffs sands in order to reach the beach. Vegetation was planted to increase the shear strength of the material; willow stems were embedded into sand using pins driven into the slope. (planted along the contours of the cliffs and anchored to pins driven into sand)

Answer 46

A relatively large sand fan left behind after a section of the cliff behind Cecil Green Mansion collapsed in 1994

Answer 47

use the sands dredged from the Fraser River to cover and widen the beaches so that waves would break further from the cliff base. These sands would be reworked and eroded relatively quickly as demonstrated by the undermining of the 1974 berm

Answer 48

private hydroelectric energy company in northern Italy

Answer 49

265.5 m. Tallest concrete arch dam in the world.

Answer 50

Provided employment for 400+ people. Valley population: 2000+ people.

Answer 51

He concluded that some local detachments of material of the reservoir slopes could be expected, but not serious. These investigations (reservoir slopes) only included the lowermost sections of the slopes.

Answer 52

He investigated during the the filling of the reservoir. His investigations contradicted Dal Piaz's favorable report, uncovering a prehistoric slide of unknown dimensions on the left reservoir slope.

Answer 53

the left reservoir slope

Answer 54

Because plans were underway to nationalize the production of hydroelectric energy in Italy, where existing structures would be sold to the state. For Vaiont, a working plant would be worth much more than an untested plant.

Answer 55

A 2-km long tension crack opened near the top of the slope suggesting that a very large landslide had been mobilized. Later, with the depth of the reservoir at 180 m, a large landslide occurred when 700,000 m3 of material slid into the lake in about ten minutes killing a worker. Lowering of the dam was ordered.

Answer 56

One year later, the 700 m level was reached completing the second water test, and the filling of the reservoir stopped. This was an important milestone as the federal law to nationalize hydroelectric production in Italy was finally issued in December 1962. Meanwhile, the water level was lowered stopping at 648 m on early 1963.

Answer 57

Slope movements resumed. Water level was quickly dropped to bring the slope under control. However, unlike previous experiences where such action helped halt the slope movements, this time velocities continued to accelerate.

Answer 58

Letter addressed to call back from vacation his chief of construction. Translational speeds within the landslide have increased. Ruptures in the terrain and road, evident inclination of trees in the area over La Pozza, enlargement of the large scarp around the mountain, motion of points near Pineda (which had been stable). Water level going down, intended to reach 695m in level to create a safety margin in the eventuality of waves.

Answer 59

at night, on Oct 9 1963..

Answer 60

260 million m^3 of rock

Answer 61

30 m/s northwards, completely blocking the gorge

Answer 62

50 million m^3 wave of water. Half of it was pushed over the dam.

Answer 63

The water then fell vertically, 261 meters into the narrow valley forming a 70 m high wave traveling at about 100 km/h. At about 22:40, about 1 minute after the detachment of the landslide, a wind began to blow across Longarone and mud began to rain down. Three minutes later the wave reached the centre of the valley and with a height of still 30 m, hit Longarone and a series of neighbouring towns. The numbers vary, but approximately 1,900 people were killed in the towns below the dam.

Answer 64

1900 people

Answer 65

2 days after the disaster, ENEL/ SADE released a statement saying that "the landslide was not predictable"

Answer 66

March 22, 2014 at 10:37am. 45 days of heavy rain.

Answer 67

layers of glacial sediments, which sent mud and debris south towards the Stillaguamish River.

Answer 68

An entire rural neighborhood drowned in the mud. 43 deaths, 49 homes destroyed, and other buildings too. Mudslide dammed Stillaguamish River, flooded highways and settlements upstream. US $10 million loss. Deadliest single landslide event in the history of the US.

Answer 69

Oso Mudslide, on March 22 2014, 10:37am.

Answer 70

The controversial part of this disaster was that government officials insisted that "This was a completely unforeseen slide. This came out of nowhere", when in fact geologists, engineers, and even local residents were very much aware of the history of slides in the area. A local newspaper article questioned "Unforeseen' risk of slide? Warnings go back decades" while a government official stated "A slide of this magnitude is very difficult to predict. There was no indication, no indication at all."

Answer 71

Indeed, the history of slides in the area is long. 1937: aerial photographs show active landslides; 1949: A large landslide (300 m long and 800 m wide) affected the river bank; 1951: Another large failure of the slope; the river was partially blocked; 1988: Erosion of the toe leads to another slide. River pushed South again; 1999: US Army Corps of Engineers report warns of “the potential for a large catastrophic failure”; 2006: large slide blocks the river, a new channel is cut to alleviate flooding; 2010: Study commissioned by the county, warns hillside above a local road is "...one of the most dangerous in the county".

Answer 72

In a report by the Geotechnical Extreme Events Reconnaissance (GEER), a team of scientists and engineers tasked to evaluate natural disasters, the 2006 landslide likely was a recursor for the much bigger slide. This slide created an uncompacted layer of rocks and soil that readily soaked up water and was thus more prone to failure. The 45 days of heavy rains prior to the disaster soaked up the region. According to the report, the slide was in fact two interconnected events: (1) the debris field from the 2006 landslide liquefied. (2) That process sent a mass of mud and debris shooting across the valley, taking with it support for a large chunk of the mountain. The mountain side fell away and became part of the slide.

Answer 73

a team of scientists and engineers tasked to evaluate natural disasters