1995 La Conchita landslide in California The community of La

1995 La Conchita
landslide in California
08CO, p.187
The community of La Conchita, California-soft marine terrace above it gave way when
soaked with too much water
Fig. 8-1a, p.188
Fig. 8-1b, p.188
talus slope of basalt blocks formed as rocks fell from the
cliff and rolled down the slope to rest at their angle of
repose (Columbia River Plateau near Palouse Falls, WA).
Fig. 8-2, p.189
irrigated avocado field is
visible at the top of the
terrace in this
photograph, which was
taken the day after the
landslide in 1995
forces on a mass
resting on a slope
steeper slope has a larger
force parallel to the slope
(red arrow)
the main features of a rotational landslide
Fig. 8-3, p.189
for the gentler slope, the friction
force (f) is larger than the force
pulling parallel to the slope (F),
Fig. 8-4, p.190
Capillary cohesion in the narrow necks
between grains pulls the grains together.
Fig. 8-5, p.191
Water (dark) seeps out of the soil below the sharply
defined saturation level exposed in a road cut in Glacier
Fig. 8-7, p.191
National Park, Montana
Filling a reservoir behind a dam raises groundwater
in the adjacent slopes, often leading to sliding into
the reservoir
Fig. 8-9, p.192
Water pressure at depth is equal
to the load or weight of the
overlying water.
Fig. 8-6, p.191
1999 Dana Point landslide north of San Diego, California
Fig. 8-8, p.192
Installation of a perforated drainpipe can lower
the water table and reduce the chance of
sliding.
Fig. 8-10, p.193
Low permeability of this shale necessitates many
drainpipes
Water drains from perforated groundwater-drainage
pipes in shale road cut on U.S. Highway 101 north of
Garberville, California
Loosely packed grains provide large pore spaces for
water. If the grains collapse to a tighter arrangement,
much of the water must be squeezed out.
Fig. 8-11, p.193
Fig. 8-12, p.194
houses on San
Francisco Bay fill did
not collapse during
the 1906 earthquake
but settled as the fill
liquefied
Three typical types of ground failure during liquefaction
Fig. 8-13, p.194
Fig. 8-14, p.195
http://en.wikipedia.org/wiki/Quick_clay
http://geotechnical.ce.washington.edu/courses/cee522/RissaLandslide/rissa.h
tml
Clay grains deposited in random orientation have
especially large pore spaces—a “house of cards”
arrangement. After collapse, compacted clays take up
much less space so water in pore spaces must escape.
Fig. 8-15, p.195
Lemieux flow in a horizontal terrace of the Leda Clay of
the St. Lawrence River Valley near Ottawa, Ontario,
settled and flowed into the adjacent river on 6/20/93
Fig. 8-16, p.195
http://geotechnical.ce.w
ashington.edu/courses/
cee522/RissaLandslide/
rissa.html
Rissa Landslide, 1978
near Rissa Norway
The Northridge earthquake caused a
Fig. 8-17a, p.196
swarm of landslides
Mitigation: installing
heavy wire mesh over
a dangerous rockfall
area above the Trans
Canada Highway.
Magn. 7.9 earthquake on the Denali Fault 2003 caused
Fig. 8-17b, p.196
landslide onto Black Rapids Glacier, Alaska Range
Workers drill and bolt a rock cliff above Highway 1 at
mouth of Topanga Canyon, CA, west of Los Angeles
Fig. 8-19a, p.197
Fig. 8-18, p.196
Rockbolts and shotcrete stabilize a heavily fractured
road cut below houses in Acapulco, Mexico
Fig. 8-19b, p.197
Subsidence and seaward spreading of the
marine terrace in Anchorage
Steeply dipping limestone beds
slope toward and daylight over
a coastal highway near
Sorento, Italy
This dropped trough formed at the head of the L Street
Fig. 8-20, p.197
landslide
Fig. 8-21, p.197
Subtle evidence!
hummocky landslide terrain is near Gardena, north of
Boise, Idaho
Fig. 8-22, p.198
Table 8-1, p.199
Marble Canyon,
Arizona, recent
rockfall debris forms
talus fallen from the
visible scar on the cliff
above.
North Cascades HWY November 10, 2003
Fig. 8-23, p.199
Fig. 8-24, p.199
Some rockfall
problems arise where
a strong layer such
as sandstone overlies
a weak layer such as
shale or clay in
Pennsylvania.
Fig. 8-25, p.200
A 4.5-meter boulder crushed the living room,
bathroom, and part of the bedroom of this house at
Rockville, Utah, near Zion National Park at 5:38 A.M.
on October 18, 2001.
Fig. 8-26, p.201
“runout” distance traveled by a debris avalanche depends
principally on the height of the mass before it falls and
therefore its potential energy. The values are variable, but
an approximation is provided by the formula above:
Sidebar 8-4, p.200
The source of the
boulders was a
massive sandstone
and conglomerate
cliff above the
location shown in
Figure 8-26. The
boulder is partly
visible middle right.
The man at left
provides scale.
Fig. 8-27, p.201
layers and parallel orientation of
micas in the schist almost parallel
to the slope at Madison slide
headscarp.
a)The Madison slide collapsed into
the Madison River canyon and
continued upslope to the north, left to
right. It dammed the river to form
Earthquake Lake
Fig. 8-28a, p.202
Fig. 8-28b, p.202
Frank slide peeled off the whole east face of Turtle
Mountain and spread a bouldery limestone deposit
across the valley and up the slope to the west. Fig. 8-29, p.203
slope before and after the Frank slide
Fig. 8-30, p.203
Mount Nevados
Huascarán debris
avalanche in 1970 buried
the town of Yungay
cross section shows the Elm, Switzerland, debris
avalanche and the location of the slate quarry that
set it off.
Fig. 8-31, p.204
Mclure slide south of Aspen, Colorado, is notorious for
continuing to slide. The car plunged off the severed
Fig. 8-33, p.206
road in 1994
Fig. 8-32, p.205
Rotation of a slump block
Blackfoot landslide in Montana
Fig. 8-34, p.206
A house begins to break up in a series of rotational slumps in
Colorado River bluffs, Grand Junction, Colorado
Fig. 8-35, p.207
Fig. 8-36, p.207
Heavy boulders are often piled on the
lower part of a slide to resist movement.
This road, cut through a landslide on U.S.
Highway 101 near Garberville, in northern
California
Crushed rock is scattered along the failure surface of a
landslide at Newport, Oregon (see arrow).
Fig. 8-37, p.208
Fig. 8-38, p.208
sackung
features
in the high mountains of
British Columbia
A section of coastal cliff at the edge of
Puget Sound, near Seattle, collapsed,
crushing and burying a home on the
narrow strip of beach
Fig. 8-39, p.208
Fig. 8-40, p.209
$400 million = most
expensive single
landslide event in
U.S. history
The 1983 Thistle landslide se of Salt Lake City, Utah, began in response to
rising groundwater levels from heavy spring rains Within a few weeks, the slide
dammed the Spanish Fork River and took out U.S. Highway 6 and a major
Fig. 8-41, p.209
railroad line. Water behind the slide dam submerged the town of Thistle.
October 1985, a landslide destroyed 120 houses in Mamayes,
Puerto Rico, and killed at least 129 people. The catastrophic block
slide was triggered by a tropical storm with extremely heavy
Fig. 8-42, p.209
rainfall
Slumgullion earthflow of southwestern Colorado --volcanic rock
peaks in the background are heavily altered to slippery clays,
Fig. 8-43, p.209
spreading out into Cristobal Lake in the lower right
Aldercrest landslide in southwestern Washington
at Kelso; > 60 homes destroyed
Fig. 8-44, p.209
disastrous 1963 Vaiont slide in northeastern Italy
moved catastrophically on weak layers of shale
within limestone beds parallel to the mountain face
Fig. 8-45, p.210
north–south cross section
shows the Vaiont Reservoir
area, preslide mass, and
Fig. 8-46, p.211
landslide
stronger layer over weak clays may fail by lateral
spreading. Parts of the spreading mass may drop as it
spreads.
Palm Springs
Fig. 8-47, p.212
Fig. 8-48, p.212
debris flows from the huge fault scarp of the Wasatch
Front behind Salt Lake City, Utah, in 1983
Fig. 8-49, p.212
1996 debris-flow channel, a tributary to the Columbia
Fig. 8-50, p.213
River, near Dodson
debris flow in the Andes of
northwestern Argentina
Slide Mountain, Nevada, southwest of Reno in May of
1983
Fig. 8-51, p.213
Fig. 8-52, p.213
This diagram shows the distribution of
grain sizes and water in a debris flow.
Fig. 8-53, p.214
May 1998, a muddy debris flow from the steep hillside to
the right of this house in Siano, Italy, east of Mount
Fig. 8-54, p.215
Vesuvius
The small
community of
Orting,
Washington, is
built on huge
mudflows that
poured down a
valley from
Mount Rainier
500 years ago.
Earlier mudflows
filled the same
valley;
undoubtedly,
mudflows will do
so again
House buried by debris flow
Fig. 8-55, p.215
Fig. 8-56, p.215
The end of this apartment
building on the
Caraballeda fan collapsed
when debris-fl ow boulders
crushed key support
columns. The largest
boulder is more than 2
meters high.
May 1998, a muddy debris flow from the steep hillside to
the right of this house in Siano, Italy, east of Mount
Vesuvius
Fig. 8-57a, p.216
Fig. 8-57b, p.216
Venezuela were crushed as the slopes gave way in the
Fig. 8-58, p.217
saturating rain
1978 storm filled the basin behind this debris- flow dam
Fig. 8-60, p.218
and overtopped the dam at La Crescenta, California.
Note abrasion line
on trees
Tumalt Creek, east of Portland, Oregon
A modern debris-flow collection basin was built in Rubio
Canyon, north of Pasadena, California.
Fig. 8-59, p.218
Debris basin north of Pasadena
Fig. 8-61, p.218
Sleeping Child Creek,
south of Hamilton,
Montana, in July 2001;
Note scarring and
abrasion of bark.
Fig. 8-62, p.219
Fig. 8-63, p.219
fast-moving mudflows racing right to left down the valley
from Mount Pinatubo in the Philippines
Fig. 8-64, p.220
Soil creep produces a
slow downslope
movement of the
upper layers of soil or
soft rocks.
A large earthquake on January 13, 2001, triggered this
devastating mudslide in a middle-class subdivision in
Colonia Las Colinas, El Salvador. It killed ~585. Fig. 8-65, p.220
Pistol-butt trees are
often a signal of soil
creep
Fig. 8-66, p.221
Fig. 8-67, p.221
Fig. 8-68, p.221
Table 8-2, p.222
distribution of landslide-prone
areas in the United States.
Table 8-3, p.223
hummocks deposited as a massive landslide from Mount
Shasta, visible in the upper left. This slide occurred
between 300,000 and 380,000 yr ago and was 25 km3
Fig. 8-70, p.225
Fig. 8-69, p.225