Session II. NATURE & CHARACTERISTICS OF NATURAL AND MAN-MADE HAZARDS

A. Natural Hazards

1. Types of Natural Hazards

a. Geological and Seismological Hazards

a.1 Structure of the Earth
a.2 Plate Tectonics

b. Earthquake

b.1 Definition

EARTHQUAKES are ground vibrations caused by rock failure or volcanic activity.

b.2 Types of Earthquakes

The most common type of earthquake is the TECTONIC earthquakes which are produced when rocks break suddenly in response to geological forces within the earth. Another is VOLCANIC quake which occurs in conjunction with volcanic activity.

TECTONIC earthquakes occur mainly because rocks are elastic and they store energy during tectonic deformation. When this strain builds to a level which is beyond that which can be sustained by weak fractures on the earth’s surface, these fractures suddenly slip thereby producing vibrating waves that are transmitted all over the earth.

VOLCANIC quakes are those recorded from within active volcanoes and sometimes, their mechanism may be similar to that of tectonic quakes. On many occasions, however, volcanic quakes are generated by the movement of molten rock materials inside a volcano, or when magma is being extruded to the outside.

b.3 Magnitude and Measurement

b.4 Intensity and Measurement

b.5 Associated Hazards

TSUNAMI - are large sea waves generated by underwater or near-shore earthquakes or volcanic eruptions. Not all submarine earthquakes or volcanic eruptions, however, cause tsunami. Tsunami occur only when the event is strong enough to cause sea floor displacement and disturb the mass of water over it such that a series of large waves are generated. Other sources of tsunami had been observed. These include submarine or coastal landslides, pyroclastic flows from oceanic or partly submerged volcanoes, caldera collapse and mudflows entering the sea.

LIQUEFACTION -
FAULTING -
SUBSIDENCE -
SAND BOILS -

c. Volcanic Eruption

c.1 Definition

VOLCANIC ERUPTION is the process wherein molten rock materials (collectively called magma or lava) are emitted or ejected in the form of flowing masses (lava flows and pyroclastic flows), discrete particles (volcanic ash and pyroclastic) and steam (water vapor and gases) from a crater, vent or fissure.

c.2 Types of Volcanoes and Eruptive Activity

c.3 Warning Phases

	Permanent Danger Zone
Restrictions	· Permanent habitation not allowed · Kaingin is restricted · People’s access discouraged · Off-limits to
Phase 1	Danger Area
Restrictions	· Limited habitation allowed · Evacuation measures implemented during eruptions · Establishment of heavy industries and populated facilities are discouraged Access may be limited, depending on intensity and character of eruption
Phase 2	Danger Area
Restrictions	· Habitation allowed · Evacuation may be recommended on selected sites depending on intensity and character of eruption
Phase 3	Danger Area
Restrictions	· Evacuation and access limited according to intensity and character of eruption

c.4 Associated Hazards

There are several processes that occur on the slopes of the volcano that pose hazards to man and his environment. Most of the hazards are directly caused by volcanic eruptions which usually involve expressive flows of hot and usually molten materials out of the volcano’s crater. Lava flows and pyroclastic flows are the main volcanic hazards. The effects that can be expected from these are the damage and injury or death by impact, incineration, burial and bulldozing.

Another hazard that is also directly related to volcanic eruption is the fall of volcanic materials ejected from the crater. The size of these materials vary and range from large “volcanic bombs” to small dust-sized particles called “volcanic ash.” The distance reached by these particles falling nearer the source and the smaller ones farther away, the intensity of the eruption, and wind velocity and direction. The effects that may be expected from these falling materials is hot, burial from substantial deposits and respiratory complications from inhalation of the fine particles.

Other hazards that may be directly associated to volcanic eruptions are the occurrence of strong earthquakes, fissuring of the ground and the generation of tsunami and seiches for volcanoes in or near the sea or lakes.

Some hazards are indirectly related to volcanic eruptions. These include the hazards from volcanic mudflows or lahars. Lahars occur when the loose materials on the volcano’s slopes are mobilized by heavy rainfall causing a river of high density mud to flow. These lahars travel with velocities from 5 to 20 m per second and usually reach as far as the sea. Landslides and debris avalanches are the other hazards that may occur even without volcanic eruptions. The effects that can be expected from these debris flows and slides are damages and injuries resulting from the bulldozing effect of the flow or slide, burial by the deposit, erosion and impact of the large boulders that accompany the materials.

(Pyroclastic Flow, Ashfall, Mudflow “Lahar”, Ballistic Bombs, etc.)

B. Meteorological & Hydrological Hazards

1. Meteorological

a. Thunderstorms
b. Monsoon (NE and SW)
c. Fronts (Cold and Warm)
d. Intertropical Convergence Zone (ITCZ)
e. Easterly Wave
f. Tropical Cyclones

f.1 Classification
f.2 Characteristics (Structure, Movement, Intensity)
f.3 Areas of Formation
f.4 Associated Hazards

f.4.1 Strong Winds
f.4.2 Heavy Rainfall
f.4.3 Strong Surge

f.5 Warning and Dissemination

g. Drought
h. Climate Change

2. Hydrological

FLOODS can be defined as an abnormal progressive rise in the water level of a stream that may result in the overflowing by the water of the normal confines of the stream with the subsequent inundation or flooding of the areas which are not normally submerged.

a. RIVERINE is due to overflowing of river banks and/or protective dikes and levees.

b. FLASH FLOOD is a condition which develops into flood in a very short period of time after a rainfall event

c. STANDING FLOOD cover a wide continuous area and rapidly spread to adjoining areas or relatively lower elevation.

d. DAM FLOODING is caused by the overflowing of rivers and lakes unexpected and serious breaks in dikes, levees and other protective structures or uncontrolled releases of dam water.

C. Man-made & Technological Hazards

1. FIRE is a chemical reaction known as combustion. It is frequently defined as the rapid oxidation of combustible material accompanied by a release of energy in the form of heat and light.

2. CIVIL STRIFE

3. OIL SPILL

4. RADIOACTIVE FALLOUT

5. BLEVE (Boiling Liquid Evaporating Vapor Explosion)

6. SEA AND AIR MISHAPS

7. POLLUTION is the undesirable change in the physical, chemical and biological conditions of the environment. It may or will harmfully affect human life, plants and animals, industrial, agricultural and commercial processes, recreational or cultural assets.

· Types of pollution

a. Air
b. Water
c. Land