Mudslides occur in a very specific set of conditions && circumstances.
An AREA prone to mudslides is a moderate or severe
slope with a fairly thick covering of loose topsoil, usually devoid of
vegetation or only sparsely covered with plants and grasses.
When this area and an area of higher elevation adjacent to it are
drenched with rain, the earth may absorb so much water that it
loses its ability to adhere to the subsoil and becomes, in effect, a
giant puddle of thick mud.

    If the mixture gets to the point where it contains as much water
as earth, the layer of mud will slide down the slope and settle in a
flat spot at lower elevation. (The first part of the above statement
is true for a mudslide that forms on a moderate slope; on a severe
slope, the mixture will slide when it contains substantially less
water.)

    If a character finds himself on a slope when a mudslide begins
to occur, he will be unable to avoid being carried down the slope
unless the area contains some solidly rooted vegetation (a tree or
a large shrub) that he is able to grab.

    The trip down is dirty but not, under normal circumstances,
dangerous; a character will not take abrasion damage from a
muddy tumble, nor will be suffer impact damage at the end of the
ride. But if the mudslide ends in a deep valley where a significant
depth of mud can collect, a character may sink into the mire and
suffocate. A character with swimming proficiency can stay on top
of the mud indefinitely, as long as his present condition of encumbrance
enables him to swim, and can make his way along the surface
at 1“ per round in an attempt to get to safety. A character
without proficiency in swimming can “tread water” on top of the
mud for half as long as he is able to stay afloat in water; after that,
he must make a Strength Check once per round. Failure indicates
that he has sunk beneath the surface. He can survive for at
least as long as he can hold his breath, and when that time limit
expires he must make CON Checks (as described in the
text on "Holding One's Breath" in the section on Swimming) to
stay alive.
 

Natural Hazards in the Wilderness

WSG