Runout of a large landslide. Consider a landslide mass that fails from an elevation
of 2500 m. The valley floor onto which the rockmass tumbles lies at 1700 m.
The mass comes to a screeching halt on the opposite valley wall at an
elevation of 1950 m.
Calculate the maximum and minimum speed at which the mass is traveling as it
crosses the valley floor.
Given these estimates, estimate how much time a citizen of the valley floor would
have to get out of the path of the slide if they were fortunate enough to have
witnessed its initiation.
Conversion of potential energy to kinetic energy
Mechanical Work = Change in Energy
Units of force (lb or Newton times distance) = kg x m2/s2
PE = KE
mgz 
v
1
2
mv
2 gz
2
v  125 m / s
T  v / dist 
800 m
1

s
125 m
 6 .4 s
Mass wasting features
• Brook, question 7.1, King Hill, ID
– 7.1a
• What type of mass movement occurred and how
did it happen? rotational block slump
• Did debris reach King Cr? If so, where? Give
coordinates. yes, at A.0-3.0 to A.4-3.4
– 7.1c
• Three well-defined slump blocks are visible in the
middle photo. Give their grid coordinates.
C.9-2.1 or E.0-2.1
• Brook, question 7.2, Slumgullion, CO
– 7.2a
• What kind of mass movement occurred?
earthflow (more soil than rock/soil mix)
– 7.2b
• What relationship is there between the moved
material and Lake San Cristobal?
earthflow dammed the river creating Lake San Cristobal
Mass wasting features
• Brook, question 7.3, Sundog Basin,
Canada
– What type of mass movement has occurred in
the unconsolidated sands (D.1-2.0)?
rotational soil slump
– What could have triggered it?
erosion of the slope toe by the river
reduced support at toe and weight of
overlaying material triggered failure
Gladstone, Oregon