The debris flow can be divided into three categories according to
their material composition: Composed of sand grains and stones,
which are full of large amount of viscous soil and grain sizes,
are called mudslides. Mainly composed of sticky soil, containing a small
amount of sand, stone, and mud with large viscosity, it is called mud flow.
Consisting of water and grains and stones of unequal size,
it is called water-rock flow.
Mudslides can be divided into two categories according to
their physical state: one is the viscous debris flow with
a large amount of viscous soil. Its characteristics are:
the viscosity is large, solid material accounts for 40% ~ 60%,
with the maximum is 80%. The water is not the carrying medium,
but the composition of the material. The consistence is large and
the rock is in suspension. This kind of mudslide outbreaks suddenly
and lasts for a shor time with destructive power.; The second is the
dilute debris flow, with water as the main component and small amount of
viscous soil and 10% ~ 40% of solid material, which is very dispersive.
The water is a moving medium and the rock moves in a rolling or jumping way
with a strong downcutting effect. Its accumulation in the accumulation area
is like a fan and after the deposition, like "stone sea".
The above categories are the two most common categories in our country.
There are many other ways to categorize. According to the causes of
debris flow, there are: water stream debris flow, debris flow of rainfall
type; According to the size of debris flow basin, there are:
large debris flows, medium and small debris flows; According to
the development stage of debris flow, there are: debris flow
in developing, mudstone flow in prosperous period and debris flow
in decline phase.
On the morning of August 14, 2002, a debris flow occurred in the area
that is 30 kilometers long and 8 kilometers wide from Ailao Mountain to
Gasa River in Yunnan. 4008 houses were damaged and 40 people died
and 23 people lost. The affected population reached 29160 in total.