Geologic Hazards PDF

# Geologic Hazards A geological hazard is a condition or event that may cause harm to property and life as a result of a geological process such as earthquake, volcanic eruption, or landslide. ## Geologic Hazards - **A. Earthquake** - **B. Volcanic Eruption** - **C. Landslides** ### A. Earthquak...

# Geologic Hazards A geological hazard is a condition or event that may cause harm to property and life as a result of a geological process such as earthquake, volcanic eruption, or landslide. ## Geologic Hazards - **A. Earthquake** - **B. Volcanic Eruption** - **C. Landslides** ### A. Earthquake An earthquake is a feeble shaking to violent trembling of the ground produced by the sudden displacement of rocks or rock materials below the earth's surface. There are two types of earthquakes: tectonic and volcanic earthquakes. Tectonic earthquakes are those generated by the sudden displacement along faults in the solid and rigid layer of the earth. Earthquakes induced by rising lava or magma beneath active volcanoes are called volcanic earthquakes. #### Most common earthquake-related hazards: - **Ground shaking** is a disruptive up-down and sideways movement or motion experienced during an earthquake. Strong ground shaking can cause objects to fall, break windows among others. - **Ground rupture** is displacement on the ground due to movement of fault. This will be experienced by areas where fault passes [through. Note, not all cracks on the ground that people see after a strong earthquake are faults, some may just be superficial cracks because of ground failure]. The movement may have vertical and horizontal component and may be as small as less than 0.5 meters. - **Tsunami** is a set of sea waves resulting from the disturbance of ocean floor by an earthquake. This is a series of giant sea waves commonly generated by under-the-sea earthquakes and whose heights could be greater than 5 meters. - **Liquefaction** 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. - **Earthquake-induced landslides** are failures in steep or hilly slopes triggered by an earthquake. Loose thin soil covering on the slopes of steep mountains are prone to mass movement, especially when shaken during an earthquake - **Fire** is caused by rupture of gas lines during ground shaking and displacement. It poses threat of explosions which may cause death and destruction of property. ### B. Volcanic Eruption Volcanic eruption happens when materials such as magma, ash, and gas are released from a volcano due to a buildup of pressure inside. The effects of an eruption can be on a local scale affecting the areas near the volcano (e.g. lava flow reaches nearby towns) or on a global scale (e.g. volcanic ash particles on air change global temperature). #### **Common volcanic hazards:** - **Lahar** is a mixture of volcanic debris and water that flows at the slopes of the volcano. It destroys infrastructures, buries towns and crops, and fills river channels. - **Pyroclastic fall** is a mass of hot, dry pyroclastic material (mixture of ash and dust) and hot gases. It moves rapidly along the ground surface. It buries towns and causes burns, injury, and damage upon impact. - **Volcanic gases** are vapors released during an eruption. Some of these gases, such as hydrogen sulfide ( H2S) and sulfur dioxide (SO2 ), are poisonous. They cause respiratory damage and death. - **Tephra falls** are rock fragments and lava blobs ejected by a volcano. They damage structures, break power lines, kill vegetation, and cause respiratory damage. ### C. Landslides A landslide, also called landslip, occurs when earth materials (rocks, debris, and soil) move downwards along a slope. It may be caused by earthquakes or heavy rainfall. It can also be aggravated by human activities such as deforestation, blasting, and construction. Landslide hazards are events associated with a landslide that may cause adverse effects on organisms and their environment. #### **Common landslide hazards:** - **Mud flow** is the flow of mud and rock. It may pick up trees, houses, and cars as it moves down the slope. It may block bridges and tributaries causing flood along its path. - **Earthflow** is the downward flow of fine-grained materials, such as clay, fine sand, and silt. It is slower than mudflow, but it inflicts the same damage. - **Rock fall** is the sliding, toppling, or falling of rocks along a slope. It disrupts road traffic in mountainous regions. When it hits a structure or vehicle, it causes damage depending on the size of the rock and the force of impact.