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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