Glossary of Terms

Active Fault

It is a fault that has moved within the last 10,000 years, or in the Holocene period. It shows evidence or has documented history of its recent movement.

Active Volcano

A volcano is classified as active based on the following: (1) if it has had eruptions in historic times supported by numerous historical accounts; (2) if it has oral folkloric history which suggests an eruption that are remembered by our ancestors; (3) if it has shown indications of seismic activity and (4) if it has volcanic deposits less than 10,000 years as determined by radiometric dating.


It is also known as tephra fall. This is the showering of fine-to-coarse-grained volcanic material and other airborne products of a volcanic eruption. Its distribution or dispersal is dependent on prevailing wnd direction.

Ballistic Projectiles

These are large particle tephra called volcanic bombs that are too heavy to transport in eruption columns. They are ejected straight out of the volcanic vents.

Base Surge

It is a special class of pyroclastic density current that are mobile and water-vapor-rich pyroclastic surges; They are generated by explosive phreatomagmatic eruptions.


It is a weak to violent shaking of the ground produced by the sudden movement of rock materials below the earth’s surface.

Earthquake-induced Landslide

It is the downslope movement of rocks, solid and other debris due to the failure of steep or hilly slopes triggered by an earthquake.


It is a break, fracture, fissure or zone of weakness where movement or displacement had occurred or may occur again. It may extend hundreds of kilometers across the earth's surface and tens of kilometers downward.

Geological Hazard

These are natural earth processes or phenomena such as earthquakes, volcanic eruptions, landslides that may cause the loss of life, injury, property damage, social and economic disruption, or environmental degradation.

Ground Fissuring

It is the movement/adjustments along faults, accompanied by earthquake.

Ground Rupture

It is the displacement on the ground due to the movement of fault. The movement may have vertical and horizontal component and may be as small as less than 0.5 meters.

Ground Shaking

It is the destructive up-down and sideways motion felt during an earthquake. Strong ground shaking can cause objects to fall, break windows among others and can also result to minor damages to buildings and worse, cause collapse of a structure.

Inactive Volcano

A volcano is said to be inactive if it has no record of eruptions and its form has been changed by agents of weathering and erosion with the formation of deep gullies.


It is the description of how weak or strong the shaking is. It is generally higher near the epicenter (reported as Roman Numerals e.g. I - Scarcely Perceptible to X - Completely Devastating) and this is measured by (a) what people see and feel (b) severity and extent of damage to buildings or structures; (c) condition of ground failure and presence of other earthquake hazards associated during the event.


It is a rapidly thick mixture of volcanic material and water, usually generated along river channels by extreme rainfall.

Lava Flow

This is a river of incandescent of molten rock or lava moving downslope or away from an eruption vent. It is composed of low silica magma have low viscosities and tend to flow at high speeds (kilometers per hour), while those composed of high silica magma have high viscosities and tend to move slowly (kilometers per day).


It is a process that transforms the behavior of a body of sediments from that of a solid to that of a liquid when subjected to extremely intense shaking. As a result , any heavy load on top pf the sediment body will either sink or tilt as the sediment could no longer hold the load.


It is the measure of energy released and is determined based on instrumentally derived information. It correlates with the amount of total energy released at the earthquake's point of origin and is reported as Arabic numbers for example magnitude 5.3 or 7.8.

Potentially Active Volcano

It is a volcano that is morphologically young-looking, suggesting it possibly erupted within the last 10,000 years, but has no historical or analytical records of eruption.

Pyroclastic Flow

It is a fast turbulent mass of fragmental volcanic material (ash and rocks) mixed with hot gases that flows downslope at very high speed (>60Kph).

Pyroclastics Density Current (PDC)

These are mixtures of fragmented volcanic particles (pyroclastics), hot gases and ash that rush down the volcanic slopes or rapidly outward from a source vent at high speeds.

Tectonic Earthquake

This type of earthquake is generated by the sudden displacement along faults and plate boundaries.


It is a series of sea waves generated by various geological processes and commonly generated by under-the-sea earthquakes and whose heights could be greater than 5 meters.

Volcanic Earthquake

This type of earthquake is induced by rising lava or magma beneath active volcanoes.

Volcanic Eruption

It is a process wherein molten rock materials are emitted or ejected in the form of flowing masses of lava or fragmental particles called pyroclastics with gas from a crater, vent or fissure.

Volcanic Hazards

These are phenomena arising from volcanic activity that pose potential threat to persons or property in a given area within a given period of time.

Volcanic Tsunami

It is also known as seiche which refers to the waves or waves trains that are generated by sudden displacement of water during volcanic eruptions.


This term signifies a vent, hill or mountain from which molten or hot rocks with gaseous material have been ejected. The term also applies to craters, hills or mountains formed by removal of pre-existing materials or by accumulation of ejected materials.