Geological Hazard

• Geologic hazards are events which occur irregularly in time and space and cause negative impact on man and the environment. These events involve the energy transformation of masses of soil, rocks, the lithosphere and water in various combinations and conditions.
• An important characteristic of many geologic hazards is their primeland preference—the characteristic of preferentially occupying areas targeted by man for his use.
• A geological hazard is an extreme natural events in the crust of the earth that pose a threat to life and property, for example, earthquakes, volcanic eruptions, tsunamis, ane landslides.
• An Earthquake is a natural phenomenon that occurs in different parts of the world. It can be very devastating, as it can kill thousand of people within seconds.
• Fault - a fracture in the rocks that make up the earth's crust
• Epicenter - the point at the surface of the earth directly above the focus
• Focus (Hypocenter) - The point within the earth where an earthquake rupture starts
• Plates - massive rocks that make up the outer layer of the earth's surface and whose movement along faults triggere earthquakes
• Seismic Waves - waves that transmit the energy released by an earthquake
• Intensity - measures the shaking in a certain location. Earthquakes that are shallow and near urban areas can be greatly felt even if they are weak
• Magnitude - measures the energy released at the source of the earthquake. Earthquakes that are small in magnitude and far from urban areas were barely felt, but are recorded in seismographs
• Ground Shaking - Caused by the passage of seismic waves beneath structures. As a result, these structure may tilt, split, topple, or collapse. Ground shaking is affected by how huge the earthquake is, what type of ground the earthquake waves travel through, and how far it is from the earthquake source.
• Ground Rupture - The displacement of the ground due to the violent shaking of the surface.
• Vertical displacement - occurs when one side of the ground goes up or down or both sides moved with one side going up and the other going down.
• Horizontal displacement - happens when there is a lateral movement from side to side, one side goes to the left or right, or both move sideways in different directions.
• Soil Liquefaction - occurs when a saturated or partially saturated soil substantially loses strength and stiffness in response to an applied stress such as shaking during an earthquake or other sudden change in stress condition, in which material that is ordinarily a solid behaves like a liquid.
• Tsunami - A series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater explosions above or below water all have the potential to generate a tsunami.
• Lahar Flow - A lahar is a violent type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris and water. The material flows down from a volcano, typically along a river valley.
• Pyroclastic Flow - A dense, fast-moving flow of solidified lava pieces, volcanic ash, and hot gases. It occurs as part of certain volcanic eruptions. A pyroclastic flow is extremely hot, burning anything in its path. It may move at speeds as high as 200 m/s. Pyroclastic flows form in various ways.
• Tephra Falls - All explosive volcanic eruptions generate tephra, fragments of rock that are produced when magma or or rock is explosively ejected. The largest fragments, blocks and bombs (>64 mm, 2.5 inches diameter), can be expelled with great force but are deposited near the eruptive vent.
• Ballistic Projectiles - A risk to life on active volcanoes and can cause substantial damage to exposed infrastructure and the environment due to their high kinetic energy, mass, and often high temperatures, are also common occurrences from ballistics during explosive eruptions
• Volcanic Gases - Gases given off by active volcanoes. These include gases trapped in cavities in volcanic rocks, dissolved or dissociated gases in magma and lava, or gases emanating from lava, from volcanic craters or vents. Volcanic gases can also be emitted through ground water heated by volcanic action