Geoscience Reference
In-Depth Information
Table 2.7
Examples of different types of sediment water flows and destructive mass movements in mountain environments.
Mass movement
type
Location, date
Origin
Volume
(m
3
)
Velocity
(m s
−
1
)
Travel
distance
(km)
Source
10
4
Debris flows
from superficial
deposits
Debris flows
from bedrock
failure
Gamahara
Torrent, Japan,
1996
Monument
Creek, Grand
Canyon, USA,
1984
Mount St Helens,
USA, 1980
Kautz Creek,
Mount Rainier,
Washington,
USA, 1947
Elm, Switzerland,
1881
Skei
Landslide-debris
flow
5 to 10
×
16
4.6
Marui et al.
(1997)
Debris flow
4.5
Webb et al.
(1988)
10
9
Mass movements
on volcanoes
Glacier-related
mass movements
Landslide
2.5 to 2.8
×
70 (maximum)
25
Pierson
(1988)
Driedger
(1988)
10
6
Debris flow
(glacier outburst
flood)
38
×
4.5
9
+
10
6
Rock falls and
rock avalanches
Flood
Rock avalanche
10
×
50
2
Heim
(1882)
Magilligan
et al. 2002
10
9
arársandur
jökulhlaup,
Iceland,1996
¨
Glacier outburst
3.5
×
5-10
35
+
• debris flows from superficial deposits
• debris flows from bedrock failure
• mass movements on volcanoes
• glacier-related mass movements
• rock falls and rock avalanches
Recognizing the dominant flow type that occurs
during a mountain flood event is an important
task. Differentiation of the types of water and
sediment flows, whether they are water floods,
hyperconcentrated flows or debris flows, can
be based on the degree of sorting, composition,
texture and sedimentary structures (Table 2.8,
Costa 1988). Water floods involve turbulent
Newtonian fluid flow with non-uniform sedi-
ment concentration profiles with sediment con-
centrations less than 40% by weight. Debris flows
on the other hand are rheologically very different.
They are non-Newtonian having laminar flow and
uniform sediment concentration gradients, with
sediment concentrations varying from 70 to 90%
by weight. Hyperconcentrated flows are transi-
tional between these two extremes and, as such,
retain some characteristics of both water floods
and debris flows (Costa 1988; Table 2.7).
Furthermore debris flows are often considered
as an intermediate phenomenon between hyper-
concentrated flows and landslides, both in terms
of their initiation mechanism and dynamics.
Coussot & Meunier (1996) propose a simple
scheme for classifying mass movements and
flows that occur on natural steep slopes. This is
based on material type and proportion of solid in
the moving mass (Fig. 2.10). Material types vary
from fine, cohesive clays to coarse, cohesionless
granular materials, and solid content generally
increases from water flow, to hyperconcentrated
flows, to debris flows and landslides. This is a
useful summary of many of the main slope and
valley processes that operate in mountain envir-
onments and how they are interrelated in terms
of sedimentary continua, e.g. solid:water ratio
(Table 2.7).
2.3
PROCESSES AND IMPACTS
-
EVENTS RELATED TO
NATURAL DISTURBANCE
This section will focus on natural changes in
mountain sediment systems, particularly glacier
and slope systems, that make up the coarse debris
and fine sediment components of the sediment
cascade model (Caine 1974).
