Debris flows involve the downslope movement of unconsolidated
regolith, most of which is coarser than sand. Some
debris flows begin as slumps but then continue to flow downhill
as debris flows. They typically fan out and come to rest
when they emerge out of steeply sloping mountain valleys
onto lower-sloping plains. Rates of movement in debris flows
vary from several feet per year to several hundred miles per
hour. Debris flows are commonly shaped like a tongue with
numerous ridges and depressions. Many form after heavy
rainfalls in mountainous areas, and the number of debris
flows is increasing with greater deforestation of mountain
and hilly areas. This is particularly obvious on the island of
Madagascar, where deforestation in places has taken place at
an alarming rate, removing most of the island’s trees. What
was once a tropical rain forest is now a barren (but geologically
spectacular) landscape, carved by numerous landslides
and debris flows that bring the terra rossa soil to rivers, making
them run red to the sea.
Most debris flows that begin as rock falls or avalanches
move outward in relatively flat terrain less than twice the distance
they fell. Internal friction (between particles in the flow)
and external friction (especially along the base of the flow)
slow them. However, some of the largest debris flows that
originated as avalanches or debris falls travel exceptionally
large distances at high velocities—these are debris avalanches.
Tidak ada komentar:
Posting Komentar
Catatan: Hanya anggota dari blog ini yang dapat mengirim komentar.