DRRR FINALS

Volcanic eruption

happens when lava and gas are discharged from a volcanic vent

Consequence of volcanic eruptions

• population movements as large numbers of people are forced to flee moving lawa flow

• temporary food shortages

• volcanic ash landslides called LAHAR

volcanic hazards

2phenomena arising from volcanic activity that pose potential threat to persons or property in a given area within a given period of time

how many active volcanoes does the philippine have?

24 active volcanoes

the government agency who monitors volcanic hazards is called

PHILVOCS (Philippine Institute of Volcanology and Seismology)

volcanic-related hazards

• lava flows

• ash fall or tephra falls

• pyroclastic flow and surges

• lahars

• volcanic gases

• volcanic landslide

• ballistic projectiles

• tsunami

lava flow

• intense heat of lavas can melt and burn

• they can burn forests, built up areas and houses

ashfall or tephra fall

• showers of airborne fine-to coarse- grained volcanic particles that fallout from the plumes of a volcanic eruption

• dependent on prevailing WIND direction

• endanger life and property with excessive ash, causing poor low visibility (driving, slippery roads)

pyroclastic flow

• turbulent mass of ejected fragmented volcanic materials (ash and rocks) mixed with hot gases that flow downslope at very high speeds

• surges are more dilute, more mobile derivatives

• potentially destructive owing to their mass, temperature, high velocity and great mobility

• flows can destroy anything on its path, but sites with hot rock debris, burn forests, farmlands, destroy crops and buildings

lahars

• rapidly flowing thick mixture of volcanic sediments (from pyroclastic materials) and water, usually triggered by intense rainfall during typhoons,moonsoons and thunderstorms.

• can occur immediately after an eruption or can become a long-term problem

volcanic gases

• gases and aerosols released into the atmosphere which include water vapor, hydrogen sulfide, sulfur dioxide, carbon monoxide, hydrogen chloride, hydrogen fluoride

• SO2, CO2, and HF are gases that pose hazard to people, animals, agriculture, and property

ballistic projectiles

• volcanic materials directly ejected from the vent with force and trajectory

tsunami

• sea waves or wave trains that are generated by sudden displacement of water (during undersea eruptions or debris avalanches)

impending signs of volcanic eruption

• ground deformation

• geochemistry - gas emissions from volcanoes

• seismic activity

landslide

• movement of a mass of rock, debris, or earth down a slope

• type of “mass wasting”

• down-slope movement of soil and rock due to gravity

• has multiple causes

3 major causes of landslides

• geology - characteristics of the material itself (the rock might be weak)

• morphology - structure of the land (ex: slopes that lose their vegetation to fire or drought)

• human activity - agriculture and construction, irrigation, deforestation, excavation and water leakage

types of landslides

• falls and topples - heavy blocks of material fall after separating from a very steep slope or cliff

• translational landslide - surface material is separated from the stable underlying layer of a slope (can be due to earthquake)

• lateral spread - movement of material SIDEWAYS (can be due to earthquake)

signs of impending lanslide

• springs, seeps, or saturated ground in areas that have not typically been wet before

• new cracks or unusual bulges in the ground

• soil moving away from foundations

• tilting or cracking oc concrete floors and foundations

• broken water lines and underground utilities

• rapid increase in creek water levels

• sudden decrease in creek water levels

sinkhole

a depression in the ground that has no natural external surface drainage

sinhkholes are most common in what geologists call “karst terrain”

regions where rock below the land can naturally be dissolved by groundwater

three major types of sinkholes

• solution

• cover collapse

• cover subsidence

solution sinkhole

• areas that have very thin cover of soil on the surface exposing the bedrock below

cover collapse sinkhole

• bedrock is covered by a deep layer of soil and earth

• can create large holes in a matter of minutes

cover subsidence collapse sinkhole

• formed over a period of time

• covered by soil and materials that are not well knitted together

causes of sinkholes

-can be natural or man-made

• natural: due to erosion or underground water

• man-made: drilling, mining, construction, broken wter or drain pipes, improperly compacted soil, heavy traffic

areas that are prone to landslide hazards

• On existing old landslides

• On or at the base of slopes

• In or at the base of minor drainage hollows

• At the base or top of an old fill slope

• At the base or top of a steep cut slope

• Developed hillsides where leach field septic systems are used

areas that are typically considered safe from landslides

• on hard, non-jointed bedrock that has not moved in the past.

• on relatively flat-lying areas away from sudden changes in slope angle.

• at the top or along the nose of ridges, set back from the tops of slopes