Geology Reference
In-Depth Information
Figure 11-5:
A slide
of intact rock ma-
terial and a slump
leaving a scarp.
Flows
Mass wasting movements that move fluidly — like a liquid — are called
flows.
Different
names are attached to various flows, which describe the amount of water involved and
the sediment grain size that is moved:
Earthflow:
Earthflows are relatively dry sediments with small grain sizes (usually
clay or silt; see Chapter 7 for grain size descriptions) that move downslope. Of the
quick-moving mass wasting types, earthflows are the slowest (at most, moving a
few meters per year), but they're still faster than soil creep, which I describe in
the next section.
Mudflow:
Mudflows occur when sediment is mixed with water, often after a heavy
rainfall. Mudflows can vary in consistency depending on the mix of water and sedi-
ments; some are a thin, muddy fluid, and some are thick like concrete. Volcanoes
create special mudflows called
lahars
when an eruption of ash melts and mixes
with glaciers or snow on a volcanic mountain.
Debris flow:
Debris flows are mudflows of sediments that are larger than sand —
sometimes as large as small boulders. Debris flows commonly occur in mountain-
ous areas with steep slopes. Very fast debris flows down steep slopes become
debris
avalanches
when the rocks and sediments fall through the air (similar to a
rock fall).
A More Subtle Approach: Creep and Soil
Flow (Solifluction)
