C. C. LinC. C. LinCentral Geological SurveyCentral Geological Survey
Email: Email: firstname.lastname@example.org@moeacgs.gov.twWeb: http://Web: http://www.moeacgs.gov.twwww.moeacgs.gov.tw
Introduction toIntroduction toGeological Disasters of TaiwanGeological Disasters of Taiwan
1.1. The active tectonic movement and mountain building The active tectonic movement and mountain building process have resulted in highprocess have resulted in high--rise mountains and rise mountains and strongly deformed rock formation in Taiwan.strongly deformed rock formation in Taiwan.
2.2. People are threatened by a variety of geological People are threatened by a variety of geological hazards, such as earthquakes, landslides, land hazards, such as earthquakes, landslides, land subsidence, coastal erosion, and tsunami. Among subsidence, coastal erosion, and tsunami. Among them, earthquakes and landslides are the most them, earthquakes and landslides are the most disastrous and extensive.disastrous and extensive.
3.3. Various Various geoscientificgeoscientific research and monitoring research and monitoring programs have been proceeded to provide programs have been proceeded to provide comprehensive information for disaster mitigation.comprehensive information for disaster mitigation.
In the part of the most active plate boundary with frequent earthquakes and
Where do we live in? Where do we live in?
a belt with most active volcanoes, being called Ring of FireTAIWAN
Tectonic Setting of TaiwanTectonic Setting of TaiwanPart of the CircumPart of the Circum--Pacific Pacific Seismic Belt, active tectonic Seismic Belt, active tectonic movement induced frequent movement induced frequent earthquakesearthquakesLocated along the convergent Located along the convergent boundary between Philippine boundary between Philippine Sea and Eurasian platesSea and Eurasian plates Philippine Sea plate Philippine Sea plate subductedsubducted
toward N in NE Taiwan toward N in NE Taiwan Eurasian plate Eurasian plate subductedsubducted
toward E in SE Taiwantoward E in SE Taiwan Phil. Sea plate collided with Phil. Sea plate collided with
Eurasian plate in Central E Eurasian plate in Central E Taiwan Taiwan
Being the junction of Ryukyu Arc Being the junction of Ryukyu Arc and Luzon Arcand Luzon Arc
Geologic settingGeologic setting
Geologic hazards of TaiwanGeologic hazards of Taiwan
TaiwanTaiwan may be the place on Earth most vulnerable may be the place on Earth most vulnerable to natural hazards, with 73 percent of its land and to natural hazards, with 73 percent of its land and population exposed to three or more hazards;population exposed to three or more hazards;More than 90 percent of the populations of More than 90 percent of the populations of Bangladesh, Nepal, the Dominican Republic, Burundi, Bangladesh, Nepal, the Dominican Republic, Burundi, Haiti, Haiti, TaiwanTaiwan, Malawi, El Salvador, and Honduras live , Malawi, El Salvador, and Honduras live in areas at high relative risk of death from two or more in areas at high relative risk of death from two or more hazards;hazards;
----Natural Disaster Hotspots: A Global Risk Analysis, Natural Disaster Hotspots: A Global Risk Analysis, March 29, 2005, World Bank March 29, 2005, World Bank
Geologic hazards of TaiwanGeologic hazards of Taiwan
EarthquakesEarthquakes causing the most severe and extensive damagecausing the most severe and extensive damage the most hazardous geologic processes in Taiwan the most hazardous geologic processes in Taiwan
Landslides Landslides among the most wideamong the most wide--spread geologic hazardsspread geologic hazards Landslides associated with typhoon pose fatalities and Landslides associated with typhoon pose fatalities and
property lossesproperty lossesSubsidence and coastal erosionSubsidence and coastal erosion occurred very slowlyoccurred very slowly being deteriorated by human activitiesbeing deteriorated by human activities
Volcanic Volcanic erutpionerutpion no volcanic eruption record in historyno volcanic eruption record in history
Coastal erosionCoastal erosionMost of the coastal line is Most of the coastal line is subjected to erosion, due to:subjected to erosion, due to: Over excavation of river Over excavation of river
sediments to support the sediments to support the massive demand for aggregate massive demand for aggregate of concrete has reduced the of concrete has reduced the supply of coastal sandssupply of coastal sands
Land reclamation from the sea Land reclamation from the sea for industry parks and for industry parks and construction of seaports construction of seaports interfere the distribution the interfere the distribution the sediments along coast.sediments along coast.
Dams for water supply or debris Dams for water supply or debris flows control retain the flows control retain the sediments behind the dams.sediments behind the dams.
Land subsidence along the Land subsidence along the coastcoast
Land subsidenceLand subsidenceNatural compaction of sedimentsNatural compaction of sedimentsExcessive withdrawal of Excessive withdrawal of groundwater for fish farms in groundwater for fish farms in lowlow--lying areas speeding up the lying areas speeding up the subsidence ratesubsidence rateMostly occurred in coastal areasMostly occurred in coastal areas
Land subsidenceLand subsidenceCumulative subsidence since 1970s (cm) Annual subsidence rate (cm/yr)
Landslides include many types of downhill earth movements, ranging from rapidly moving catastrophic rock avalanches and debris flows in mountainous regions to more slowly moving earth slides and other ground failures.Thousands of landslides can be triggered by a single severe storm or earthquake, causing spectacular damage in a short time over a wide area.
Landslide distributionLandslide distributionSlope failures Debris flows
Causal factors of landslidesCausal factors of landslides
LithologyLithologyshale, conglomerate, slate, and schist are highly shale, conglomerate, slate, and schist are highly susceptible to landslide susceptible to landslide StructuresStructuresbedding, bedding, foliation,jointsfoliation,joints, fractures, cleavage, , fractures, cleavage, and faults etc. and faults etc. TopographyTopographyangle, aspect, shape of slopesangle, aspect, shape of slopesImproper landImproper land--useuseremoval of downremoval of down--slope supportingslope supporting
Triggering factors of Triggering factors of landslideslandslides
Heavy rainfallsHeavy rainfallsEarthquakesEarthquakesVolcanic eruptionVolcanic eruptionChange of water levelChange of water levelSnow meltingSnow melting
Annual precipitation(unit: 1,000 mm)
People living in People living in mountainous area are mountainous area are endangered by slope endangered by slope failures and debris failures and debris flows flows
Landslide disastersLandslide disasters
Landslide disasters occurred in Landslide disasters occurred in the surroundings of urban areasthe surroundings of urban areasTriggered by heavy rainfallsTriggered by heavy rainfallsMost of them can be avoidedMost of them can be avoided
Case of landslide Case of landslide triggered by typhoon triggered by typhoon
Date: 25/08/2004Date: 25/08/2004Hazard type: landslideHazard type: landslideTriggered by: Typhoon Triggered by: Typhoon AereAereLosses: Losses: Some 20 houses buriedSome 20 houses buried 22 deaths22 deaths
Area of sliding: 5.8 hectaresArea of sliding: 5.8 hectaresVolume of sliding: 1 million mVolume of sliding: 1 million m33
Water crisis caused by extensive landslidesWater crisis caused by extensive landslides
Extensive landslides in Extensive landslides in the the catchmentcatchment area of area of ShihmenShihmen ReservoirReservoirLarge amount of Large amount of sediments being carried sediments being carried into the reservoir, raising into the reservoir, raising the turbidity of the turbidity of impoundment.impoundment.Causing crisis of lacking Causing crisis of lacking water for daily use of water for daily use of millions people for 19 millions people for 19 days.days.
Cases of earthquake induced landslide (1)Cases of earthquake induced landslide (1)TsaolinTsaolin
Date: 21/09/1999Date: 21/09/1999Hazard type: landslideHazard type: landslideTriggered by: earthquakeTriggered by: earthquakeLosses: Losses: 4 houses 4 houses 36 deaths36 deaths
Area of sliding plus debris piling Area of sliding plus debris piling up: 522 hectaresup: 522 hectaresVolume of sliding mass: 120 Volume of sliding mass: 120 million mmillion m33
Geology: Dip slope consists of Geology: Dip slope consists of sandstone overlying on thick sandstone overlying on thick soft shalesoft shale
Cross sections of Cross sections of TsaolinTsaolin landeslidelandeslide
DateDate Triggering factorTriggering factor18611861 earthquakeearthquakeM 6M 6--7712/17/194112/17/1941 earthquakeearthquakeM 7.1M 7.18/10/19428/10/1942 heavy rainfallsheavy rainfalls8/15/19798/15/1979 heavy rainfallsheavy rainfalls9/21/19999/21/1999 earthquakeearthquakeM 7.3M 7.3
Historical landslide events of Historical landslide events of TsaolinTsaolin
Case of earthquake induced landslide (2)Case of earthquake induced landslide (2)ChiufenershanChiufenershan
Date: 21/09/1999Date: 21/09/1999Triggered by: ChiTriggered by: Chi--Chi earthquakesChi earthqua