Geological hazard for grade 11

1. Geological Hazard and
Hazard Map
Grade 11- Earth and Life
Science

2. Hazard
-is a dangerous phenomenon,substance,
human activity or condition that may
cause loss of life, injury or other
health impacts, property damage, loss
of livelihood and services, social and
economic disruption, or environmental
damage as defined by the United Nations
Office for Disaster Risk Reduction
(UNDRR).

3. EARTHQUAKE
• (also known as a quake, tremor or
temblor) is the shaking of the
surface of the Earth, resulting from
the sudden release of energy in
the Earth's lithosphere that
creates seismic waves.

4. FOCUS VS EPICENTER
• Focus - where the rock breaks and
seismic waves begin; can be at
deep or shallow depths.
• Epicenter – point on the surface
directly above the focus; usually
what is used to locate the
position of an earthquake.

5. A= Focus
B= Epicenter
C= Fault

6. Seismic Waves
⮚ are waves of energy that travel through
the Earth's layers, and are a result
of earthquakes, volcanic eruptions, magma
movement, large landslides and large man-
made explosions that give out low-
frequency acoustic energy.
⮚ SEISMOGRAPH - is an instrument for
measuring earthquake (seismic) waves.

7. Volcanic Eruption
A volcanic eruption is when lava
and gas are released from a
volcano—sometimes explosively.

8. How does Volcanic
Volcanoes erupt when molten rock
called magma rises to the surface.
Magma is formed when the earth's
mantle melts.
Melting may happen where tectonic
plates are pulling apart or where one
plate is pushed down under another.

9. Types of Volcanic Eruption
★ PHREATIC OR HYDROTHERMAL -An
eruption driven by the heat in a
hydrothermal systems. Hydrothermal
eruptions pulverise surrounding
rocks and can produce ash, but do
not include magma. These are
typically very small eruptions

11. Types of Volcanic Eruption
★ PHREATOMAGMATIC- An eruption
resulting from the interaction
of new magma or lava with water
and can be very explosive. The
water can be from groundwater,
hydrothermal systems, surface
runoff, a lake or the sea.

13. Types of Volcanic Eruption
★ STROMBOLIAN and HAWAIIAN- These
are the least violent types of
explosive eruptions. Hawaiian
eruptions have fire fountains and
lava flows, whereas Strombolian
eruptions have explosions causing
a shower of lava fragments.

15. Types of Volcanic Eruption
★ VULCANIAN ERUPTION- small to
moderate explosive eruptions,
lasting seconds to minutes. Ash
columns can be up to 20 km in
height, and lava blocks and
bombs may be ejected from the
vent.

17. Types of Volcanic Eruption
★ PLINIAN and SUBPLINIAN-
Eruptions with a high rate of
magma discharge, sustained for
minutes to hours. They form a
tall, convective eruption column
of a mixture of gas and rock
particles, and can cause wide
dispersion of ash.

19. Volcanic hazards directly
associated with eruption:
1. Lava flow
2. Tephra fall or ash fall and
ballistic projectiles
3. Pyroclastic density currents or
PDCs (pyroclastic flow, pyroclastic
surge, base surge)
4. Lateral blast
5. Volcanic gas

20. Volcanic hazards indirectly
associated with eruption:
1. Lahar, flooding
2. Debris avalanche, landslide
3. Volcanic tsunami
4. Ground deformation (subsidence,
fissuring)
5. Secondary explosion
6. Secondary PDCs and ash fall

21. Landslide
-mass movement of rock, soil,
and debris down a slope
due to gravity.

22. TYPES OF LANDSLIDE
A. Rotational – more resistant
rocks over underlying weaker
rocks;
B. Translational – occur in a
very wet weather when near
surface soil is
saturated;

23. TYPES OF LANDSLIDE
C. Block – moving mass move
downslope as a coherent mass;
D. Rock fall -single and small
rock falls from cliffs build up
to form talus;
E. Topple – occur when a cliff
is eroded by waves at its base;

24. TYPES OF LANDSLIDE
F. Debris flow – sloppy wet
mudflows to slurries of rock
debris similar to wet
concrete;
G. Debris avalanche – rushes
down the side of a volcano to
the valley floor;

25. TYPES OF LANDSLIDE
H. Earthflow – a downslope
viscous flow of fine -grained
materials saturated
I. Creep -slow downslope
movement of material under
gravity over a large
area

26. TYPES OF LANDSLIDE
J. Lateral spread – form on
gentle slopes and have a rapid
fluid-like flow.

27. TSUNAMI
-series of water waves caused by
the displacement of a large
volume of a body of water.

28. TSUNAMI
-May also be caused by major
earthquakes or undersea volcanic
eruption.
-It comes from the japanese word
which literally means ―harbor
wave‖.

29. TSUNAMI
-Different from tidal wave and
storm surge.

30. NATURAL SIGNS OF AN
APPROACHING LOCAL TSUNAMI
• A felt earthquake
• Unusual seal level change
(sudden sea water retreat or
rise)
• Rumbling sound of approaching
wave.

31. NATURAL SIGNS OF AN
APPROACHING LOCAL TSUNAMI
• A felt earthquake
• Unusual seal level change
(sudden sea water retreat or
rise)
• Rumbling sound of approaching
wave.