Natural Disasters. Chapter 15. Tenth Edition. Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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1 Natural Disasters Tenth Edition Chapter 15 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 10-1

2 Slides Turnagain Heights, Anchorage, Alaska, 1964 Magnitude 9.2 earthquake triggered many mass movements Glacially ground, clay-rich sedimentary rocks Sliding began after 90 seconds of shaking liquefied deep clays Rotational slides trapped deep clay layer so it deformed internally, moving block above

3 Figure 15.25a Slides Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

4 Figure 15.25b Slides Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

5 Flows Mass movements that behave like fluids internal movements dominate, slip surfaces absent or short-lived Range of: All sizes of materials Wet to dry Barely moving to > 200 mph Gradation from movement on slip surface, to no slip surface Many names: loess flow, earthflow, mudflow, debris flow, debris avalanche

6 Flows: Portuguese Bend, California, Earthflow Rock layers dip seaward, contain bentonitic clay, and ocean waves erode toe and keep ancient earthflow moving seaward Unstable land used for farming until residential development built in 1950s

7 Figure 15.27a Flows Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

8 Figure 15.27b Flows: Portuguese Bend, California, Earthflow Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

9 Figure 15.27c Flows: Portuguese Bend, California, Earthflow Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

10 Flows: La Conchita, CA, Slump, Debris Flows, 1995, 2005 Cliff behind La Conchita is ancient landslide 1995: two slow landslides destroyed 14 houses, no deaths 2005: 15% of 1995 slide mass remobilized into highly fluid debris flow, at 10 m/sec, went over retaining wall, destroyed 13 houses, damaged 23 others, killed 10 people

11 1995 Figure 15.28a Flows Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

12 2005 Figure 15.28b Flows Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

13 Flows: Long-Runout Debris Flows Most spectacular, complex movement massive rock falls that convert into highly fluid, rapid debris flows that travel far (also called sturzstroms) Rock falls and small-volume avalanches flow horizontally less than twice vertical distance of fall Very large rock falls (more than 1 million m 3 ) travel up to 25 times vertical fall have lower coefficient of friction

14 Flows: Blackhawk Event, California, 17,000 years ago Huge rock fall in San Bernardino Mountains flowed out into Mojave Desert flowed 7.5 times farther than fell, speed estimated up to 120 km/hr

15 Figure Flows Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

16 Flows: Elm Event, Switzerland, 1881 Farmers quarried slate from base of mountain until cracks opened up in hillside above Fall, jump, surge: Mass of mountain began to disintegrate as it fell Hit floor of quarry and disintegrated completely Shot out from mountainside ledge, flowed 2,230 m into valley

17 Figure Flows Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

18 Flows: Turtle Mountain, Alberta, Canada, million ton mass of dipping limestone slid down daylighted bedding surface 3,000 feet into valley Shattered, flowed 3 km across valley, 130 m up opposite side Buried southern end of town, killing about 70 people

19 Figure Flows Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

20 Flows: Nevados Huascaran Events, Peru (1 of 2) 1962: No perceptible trigger Mass of glacial ice and rock fell 13 million m 3 debris flow Debris flowed up to 170 km/hr down river valleys, killing 4,000 people 1970: magnitude 7.7 subduction-zone earthquake 135 km away Portion of peak collapsed and fell vertically 400 to 900 m Mass landed on glacier and slid

21 Flows: Nevados Huascaran Events, Peru (2 of 2) Raced up side of glacial-sediment hill, launching debris into air Rain of rocks and boulders for 4 km downslope 1970 Flow buried town and 18,000 people beneath more than 30 m of debris

22 Figure Flows Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

23 Figure (a) Map of ancient landslides in Oso, Washington area, (b) View over toe of muddy, long-runout debris flow that moved 60 mph, killing 43 people in March 2014, (c) Aerial view of muddy debris flow (center left) and landslide (center right) Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

24 Flows: Movement of Highly Fluidized Rock Flows (Sturzstroms) (1 of 2) Hypotheses for fast and far movement: Water provides lubrication and fluid-like flow But some observed flows were dry Frictional melting fluidizes moving mass But some deposits contain blocks of ice, lichen no significant heat or friction Falling mass traps air beneath and rides trapped air But Elm sturzstrom was in contact with ground Identical flow features on ocean floor, Moon, Mars (no atmosphere)

25 Flows: Movement of Highly Fluidized Rock Flows (Sturzstroms) (2 of 2) Most likely hypothesis for fast and far movement: Blocks in moving mass hit blocks in front of them, imparting kinetic energy vibrational or acoustical energy propagates as internal waves, fluidizing rock debris (acoustic fluidization)

26 Flows: Snow Avalanches (1 of 2) Behave like earth mass movements creep, fall, slide, flow Small to large, barely moving to 370 km/hr, few meters to several kilometers Small avalanches typically fail at one steep point, in loose, powdery snow, which triggers more and more snow moving downhill Usually begin when snow reaches 0.5 to 1.5 m deep Snow depth can reach 2 to 5 m before big avalanches occur, if snowflakes become rounded and packed

27 Flows: Snow Avalanches (2 of 2) Loose-powder avalanches Low cohesion with up to 95% volume as pore space Slab avalanches Slabs of snow that break free from base like translational slides, turning into flows on way down Snow mass composed of layers with different ice, snow characteristics different strength Numerous potential failure surfaces Dry snow forms faster avalanches than wet snow Avalanches may flow for many miles, up and over ridges

28 Figure A loose powder avalanche flows toward three skiers Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

29 Figure A slab avalanche is set off by a downhill skier. Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

30 Table 15.3 Avalanche Deaths in Western Canada, Activity Deaths Males Suffocation Trauma Skiing/snowboarding Snowmobiling Ice climbing Mountaineering Snowshoeing/hiking _ Working on avalanche control Total (88%) (77%) 47 0 (23%) *Out of 201 victims Source: Canadian Medical Association Journal. Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

31 Submarine Mass Movements Same mass movements occur below sea: rotational slumps in delta deposits; complex failures at subduction zones; debris avalanches slide down submarine volcano slopes; sector collapses destroy large portions of volcanoes Can cause tsunami

32 Mitigation Efforts Controlling rotational and translational landslides Unloading head, reinforcing body and supporting toe Controlling flows of earth or snow Steering flow by building walls (gabions) and digging channels Controlling rock falls Removing rock and decreasing slope angle Holding rocks in place with wire mesh nets Using fence to catch fallen rocks

33 Figure A rock wall (gabion) Mitigation Efforts Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

34 Figure How to prevent a landslide Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

35 Figure Rock bolts extend through slope into solid bedrock Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

36 Figure Retaining wall holds back sliding earth Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

37 Subsidence: Catastrophic Subsidence: Limestone Sinkholes, Southeastern U.S. Limestone forms from CaCO 3 shells of marine organisms, dissolves in naturally acidic groundwater flowing through forms extensive water-filled caverns When groundwater levels drop, caverns are empty and buoyant support of water holding up cavern roofs is removed roofs collapse, forming sinkholes

38 Figure Subsidence Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

39 Side Note: How to Create a Cave Caves usually occur in limestone Equilibrium equation to create or dissolve limestone: Ca HCO 3 CaCO 3 + H 2 CO 3 Ca is calcium ion HCO 3 is bicarbonate ion CaCO 3 is calcite (limestone) H 2 CO 3 is carbonic acid Left to right limestone is precipitated Right to left limestone is dissolved Controlled by amount of carbonic acid, which is controlled by amount of carbon dioxide

40 Subsidence: Slow Subsidence Ground surface sags gently or drops catastrophically as voids in rocks close Slow compaction of loose, water-saturated sediments or rapid collapse into caves Slow Subsidence Ground slowly sinks as fluids (water or oil) are removed from below (squeezed out or pumped) Removal of fluid volume and decrease in porefluid pressure compacts rock, lowering ground

41 Subsidence: Groundwater Withdrawal, Mexico City Aztecs built aqueducts to bring water from mountains Extraction of groundwater through wells began in 1846 Withdrew water faster than it is replenished, causing land subsidence of 10 m Groundwater withdrawal is now banned, but subsidence can not be reversed

42 Subsidence: Oil Withdrawal, Houston- Galveston Region, Texas Pumping of water, gas, oil began in 1917 Rely on groundwater withdrawals Area has sunk up to 2.7 m, renewing movement on old faults that act as landslide surfaces

43 Figure Subsidence Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

44 Subsidence: Long-Term Subsidence, Venice, Italy (1 of 2) Venice is built on soft sediments that compact under weight of city itself, as global sea level rises Venetians have been building up islands with imported sand for centuries 20 th century pumping of groundwater rate of sea level rise in Venice doubled Sea level projected to rise 50 cm in 21 st century

45 Subsidence: Long-Term Subsidence, Venice, Italy (2 of 2) Movable floodgates across entrances to lagoon Would disrupt shipping, prevent outward flow of contaminants More sediment to raise ground level Pump seawater or carbon dioxide into sand below city to pump up region

46 Figure Subsidence Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

47 Subsidence: Delta Compaction, Mississippi River, Louisiana (1 of 2) Delta: loose pile of water-saturated sand and mud compacts and sinks down Mississippi River delta underlain by 6 km thick sediments deposited in last 20 million years River position has shifted frequently and held in place now by human action

48 Subsidence: Delta Compaction, Mississippi River, Louisiana (2 of 2) New Orleans and region sinking by sediment compaction, dewatering, isostatic adjustment about 45% of city below sea level, prone to high-water surges in hurricanes

49 Figure 15.48a Subsidence Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

50 Figure 15.48b Subsidence Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.