FLOOD00566

• County: Statewide
• Title: Nature's Building Codes - Geology and Construction in Colorado
• Date: 8/1/1979
• Prepared For: State of Colorado
• Prepared By: DNR
• Floodplain - Doc Type: Educational/Technical/Reference Information

facl! Itate Its mo~ement. The rates of movement for
landslides vary from tens of feet per second to fractions of
Inches per year. Landslides can occur as r9actlvated old
slides or as new slIdes In areas not previously experiencing
them. Areas of past or active landslldlng can be recognIzed
by their topographIc and physIcal appearance. Areas
susceptIble to landslides but not previously active can
frequent I}' be IdentIfied by the slmllarlt}' of geologic
materials and conditions to aredS of known landslide
act I ~ I ty.

Consequences

Landsl Ides In the U.S. are estImated to cause more than Sl
bll I Ion a year In property damage, according to the
Transportation ResearCh30ard of the NatIonal Academy of
ScIences. ~allroads, hIghwayS, homes, ana entire communi ties
are lost to landslides ..hlch demolISh and/or bUl"Y them. In
Colorado the 19th centul"Y mining camp of 9rowns~Ille just
..est of Silver Plume Is burled beneath a rain trlggel"ed
landslide that became a debris flow. It Is no.. under
Interstate 70. LandslIdes occur commonly throughout
Colorado, and the annual damage Is estimated to exceed three
mil lion dollars to buildings alone.

These two photos sho_ the headscarp (al and toe Ib) at a
landslIde In a residential subdivision south of Oen~er.
For tunatel y, th I s s II de occurred dur I ng ut III ty pi ace'l\ant and
lot 1radlng prior to construction at homes. Geologic

26

Aggravating Circumstances
L~ndsl Ides are one of the prl'l\,ry natural processes shaping
the land. Man's activities that frequently cause significant
Increases In landslide activity Include:
I) excavation of a steep slope or
the toe of an existing land-
slide, thus removing support of
the upslope mass,
2) addItion of material to the
head (top) of a landsl Ide ..hlch
pushes the 51 Ide material
do..nslope,
3) addition of moisture to the
landslide mass, Increasing the
weight and decreasing the
strength.
The actl~ltles ..hlch tend to Increase landslide potential
Include excavation fOl" hlghlllays and houses, -!lnd earth fills
for highways and houses. lallln "'aterlng or surface drainage
diversions. and changes In ojater Infiltration rates.
Alteration of surface land use suCh as roadcuts and water
Impoundments, ..hlch allows more _ater Into the subsurface of
a Slide-prone slope, Is a mil jar contributing factor In
landslides.

lb
-
I

=--_..

.

..? ,~-'"""'
.~

. l:I,)II'

"C: ...;.,/
'~4:' . '"
.,~~."",
-' ~ --""" ..
_....~,\.. '.,

.,

,

1 . .t'''.._
'.
~

.
'J'r-. :'\0
__1'-~~ ~ .,
1\:

'''1;
..~ ,-'0

-

< .

."~

.,
r'
, .-
"

I

,

.

1
!..... r""
...

,
__:0. .
.... -o..or-
n"""-

.

-
,,'

-.....~.
# ....;...

.

f..
.. jot ~ ...-\ _.1 "",
:~~-..~'...

, .......~
....~ ,,",...
4 ..._.........

.....

-

Investigations resulted In alteratIons In the development
plan to prevent future dam~ge. Note the very gentle slopes
3t the toe at the sl Ide. Such earth ~ovements are common In
ColoradO.