Geological Hazards
This is a before and after
illustration of a debris
avalanche of Mount
Pinatubo located on the
tripoint boundary of the
Philippine provinces of
Zambales, Tarlac and
Pampanga, all in Central
Luzon on the northern
part of Luzon.
Guide questions:
1.What happened to the appearance of
the crater after the volcanic eruption?
2. What happened to the portions of the
volcano that were removed?
3. What geologic hazard could be
responsible for the movement of the
soil?
Landslide
A landslide is a ground movement on a sloping
terrain. It does not happen on flat ground
because of the angle on the ground, gravity
induces the land to move downward. It is
aggravated by rain because water is a natural
agent for erosion. If rain or any source of water
frequently flows down a sloping area, the
gravitational descent of loosened soil makes it
possible for landslide to occur.
Types of Landslide
1. Soil Creep Landslide
- is a very slow
downslope movement of
particles that occurs in
every slope covered
with loose, weathered
material (Britannica
dictionary).
2. Slumping Landslide
is a downward
movement of rock
debris, usually the
consequence of
removal of buttressing
earth at the foot of a
slope of unconsolidated
material (Britannica dictionary).
3. Debris Flow
Landslide happens
when the slope
becomes saturated with
water, this then triggers
a landslide of water-
soaked mass of
rock and soil that slides
down the slope.
4. Rock Fall
landslides are
sudden slides caused
by heavy rain the
rock on the slope
loosens and then
slides down the
slope.
Sinkhole
A sinkhole is a topographic
depression created when
groundwater dissolves the
underlying limestone bedrock.
Often known as "sink" or "doline,".
Characteristics:
• occur in areas where the soil
foundation is made of soft minerals
and rocks such as limestone, salt beds,
or any acidic rocks.
• The depth of sinkholes ranges from a
couple of meters to several mile deep.
Types of Sinkholes
1. Cover Collapse Sinkhole
It develops suddenly (over an hour
period) thus, causing catastrophic
damage.
2. Cover Subsidence Sinkhole
It gradually grows where the sediment covers
are permeable and contain sand.
3. Dissolution Sinkhole
It occurs in areas where calcareous is exposed
on the ground or where thin layers of soil and
permeable sand are also covered. Limestone or
dolomite dissolution is most intense when the
water first reaches the rock surface.
4. Artificial Sinkhole
Such types of sinks may be
caused by various human
activities, including groundwater
pumping and building.
Activity:
What I Can Do Create an evacuation plan for your
household whenever a landslide or sinkhole may
occur. Countercheck the location of your home in
google maps or you could use the Project NOAH app
of DOST and provide an escape route. Evaluate the
risk of your location to landslides and sinkholes. Use
a bond paper and make use of arrows, different
colors of ink and standard symbols for clearer
representation. Your plan should include the
following:
a. Floor plan of your household and location
of possible exit and entry points. Also
indicate blocked exits.
b. Location of your house on a geologic
hazard map.
c. A specific rendezvous point where you and
your family members will meet.
d. Include at least three exit plans from at least
three different locations of your household.
e. You must create a Legend panel to contain the
meaning of the symbols that you have used.
Symbols must include the following:
“X” - mark of areas prone to landslide and
sinkhole.
“O” - mark for evacuation areas and safe zones.
“ - - - ” - dashed lines to indicate direction of
evacuation
