暑期坡地營課程 06/08/2014 Landslide Mapping Chyi-Tyi Lee Graduate Institute of Applied Geology, National Central University, Taiwan And Construction of a Landslide Inventory

Definition of landslide: A general term covering a wide variety of mass-movement landforms and processes involving the downslope transport, under gravitational influence, of soil and rock material. (Glossary of Geology, 4 th ed.) Definition of landslide: A general term covering a wide variety of mass-movement landforms and processes involving the downslope transport, under gravitational influence, of soil and rock material. (Glossary of Geology, 4 th ed.) Introduction Types of mass-movement: Types of mass-movement: Gradual mass-movement Creep Rapid mass-movement Landslide Landslide – any large, fast mass-movement 2 Creeping slope

Introduction Types of landslide: Types of landslide: Fallslideflow Fall, slide, flow One type of landslide can trigger or change into another as it moves downslope. 3 ● Rock fall Shallow slide Deep slide Debris flow

Classification of Landslide Type of movement Type of material BedrockEngineering soils FineCoarse FallsRockfallEarth fallDebris fall Topples Rock toppleEarth toppleDebris topple Slides Rotational Rock slumpEarth slumpDebris slump Translational Few units Rock block slideEarth block slideDebris block slide Many units Rock slide Earth slideDebris slide Lateral spreads Rock spreadEarth spreadDebris spread Flows Rock flowEarth flow Debris flow Rock avalanche Debris avalanche (Deep creep)(Soil creep) Complex and compound Combination in time and/or space of two or more principal types of movement Classification of Varnes 1978 Classification of Varnes 1978 and taking into account the modifications made by Cruden and Varnes, in Some integration have been made by using the definitions of Hutchinson (1988) and Hungr et al

Geomorphic Features of Landslde 山崩的地形特徵 (Deep-seated slide)

6 Triggering Mechanism of Landslide Intense rainfall Rapid snow melt Prolonged precipitation Rapid drawdown Earthquake Volcanic eruption Thawing Freeze-thaw Ground water changes Soil pore water pressure Surface runoff Seismic activity Soil erosion Excavation Loading Draw-down Water management Mining Quarrying Vibration Water leakage Deforestation Land use pattern Pollution Physical CausesHuman Causes Adopted from: ● ● ●

7 Preparation Works for Mapping of Landslides Selection of the Type of Remote Sensing Images Selection of the Type of Remote Sensing Images Select either aerial photo or satellite images according to, (1)Availability. (2)Purpose: aerial photo for detailed mapping, satellite image for mapping of larger region and for quick mapping. Selection of the Quality of Remote Sensing Images Selection of the Quality of Remote Sensing Images (1)Least cloud cover and noise, and best homogeneity. (2)Proper sun angle so that stereoscopic feeling is good. (3)Proper resolution according to purpose. Use of False Color Image Use of False Color Image Put IR at R-band, R at G-band, and G at B-band. Because IR is sensitive to landslide, a false color image is good for recognition of landslides. True color image is not good for. (1/2)

8 Preparation Works for Mapping of Landslides Use of a Rectified Image Use of a Rectified Image A remote sensing image should be geometrically corrected and rectified by using ground control points and DEM. This could be acquired when purchasing the images. Enhancement of an Image Enhancement of an Image (1)Linear stretching (2)Gamma correction (3)Proper saturation (4)Sharpening a little bit Registration of an Image Registration of an Image Registration of an image in a GIS system using the image coordinates and projection. (2/2)

Pre-eventPost-event SPOT Images for Mapping Landslides induced by the Typhoon Aere Event

10 Recognition of Landslides on Remote Sensing Image Image interpretation may be based on image tone, shape, association, and also judgment. The landslides could be digitized in GIS, and attributes were assigned to establish a landslide map table. Image interpretation may be based on image tone, shape, association, and also judgment. The landslides could be digitized in GIS, and attributes were assigned to establish a landslide map table.

11 SPOT5 image for extraction of landslides Landslide area 1.8 ha.) (area 1.8 ha.)

12 北 橫 大 漢 溪 蘇樂橋 高 義 SPOT5 Landslide 河道沖刷 開墾 Landslide Landslide Landslide Landslide

13 Mapping of Landslides on Remote Sensing Image Landslides prior to Typhoon AereLandslides post Typhoon Aere

14 Excluding of human development with overlaying a photo- based map. Separation of a landslide deposits area with overlaying a photo-based map. Suspect landslide on imageA golf course on photo-based map Deposits locate at gentle slope Suspect landslide on image Lab Checks of Landslide Inventory Checks of Artificial Developments Checks of Artificial Developments Checks of Landslide deposits Checks of Landslide deposits (1/2)

15 Lab Checks of Landslide Inventory Checks If a Landslide Covers a Ridge Line Checks If a Landslide Covers a Ridge Line two different landslides  A landslide is commonly restrict within a slope unit or a drainage basin. A landslide covers ridge lines is unusual and need special checks. It may be separated into two different landslides, or it may be a big landslide. (2/2) Checks If a Landslide Covers a Stream Channel Checks If a Landslide Covers a Stream Channel two different landslides  A big landslide may involve small channels and gullies in the deposition area. Other landslides are restricted within a slope unit on both sides of a stream channel. It may be separated into two different landslides, or it may be a landslide dam.

Bare rock 霞喀羅古道馬鞍駐在所對岸 Field Checks Landslide Bare rocks are excluded in the landslide inventory. Bare rocks are excluded in the landslide inventory. Field checks also for confirmation of landslide type, causative factor of landslide, and others. Field checks also for confirmation of landslide type, causative factor of landslide, and others.

17 Finalization of a Landslide Inventory Finalization of a Landslide GIS Table Finalization of a Landslide GIS Table Attribution of Landslide Inventory Attribution of Landslide Inventory  Checks if a polygon is complete and clean  Checks no polygons are overlay  Checks type of landslide and others are given in the attribute of each polygon object  A single-period landslide inventory  A multi-period landslide inventory event landslide inventory  An event landslide inventory

18 Construction of an Event Landslide Inventory Method 1: Comparison of pre-event landslide inventory and post-event landslide inventory Method 1: Comparison of pre-event landslide inventory and post-event landslide inventory  Weakness: a repeating landslide may be omitted. Method 2: Direct observation on color tone change of a landslide object Method 2: Direct observation on color tone change of a landslide object  There is risk on misjudgment of color tone change. Method 3: Automatic extraction of triggered landslides by using change detection method Method 3: Automatic extraction of triggered landslides by using change detection method  This is still developing, but semi-automatic extraction is feasible now.

19 Example of Building an Event Landslide Inventory by Method 1 5,496 slides, totaling km 2 Pre-ChiChi EQ landslides Chi-Chi EQ- induced landslides (Kuohsing Quadrangle) Post-ChiChi EQ landslides

20 Event Landslide Inventory – Method 1 Case 1 Case 2 Case 3

Event Landslide Inventory – Method 1 Pre-eventPost-event New Landslide Enlarged Landslide No Change Others

22 Example of Building an Event Landslide Inventory by Method 1 Pre-event Post-eventEvent-triggered

Enlarged Landslide Event Landslide Inventory – Method Enlarged Landslide New Landslide

24 Event Landslide Inventory – Method 3 Red NIR Green Red NIR Green Change Detection Method Change Vector Pre-event image (Green band) Post-event image (Green band) Difference image (Green band)

25 NIR Red Green ＋ Upper Hemisphere ○ Lower Hemisphere Post-event image (Red band) ○ Induced landslides (lower hemisphere) Orientation of Change Vector for Induced Landslides

26 Typhoon Aere event landslide inventory after conditional screening Preliminary change points for Typhoon Aere Event Landslide Inventory – Method 3

27 Usage of a Landslide Inventory Single-period landslide inventory for susceptibility analysis may be biased in building a model. Single-period landslide inventory for susceptibility analysis may be biased in building a model. It may not be feasible to use a multi-temporal landslide inventory in some regions. There are still problems such as incompleteness of the inventory, insufficient length of historical records, and a possible mixing of extreme events and/or earthquake disturbance that need to be considered. It may not be feasible to use a multi-temporal landslide inventory in some regions. There are still problems such as incompleteness of the inventory, insufficient length of historical records, and a possible mixing of extreme events and/or earthquake disturbance that need to be considered. An event landslide inventory is good for event-based susceptibility analysis and is feasible in construction of the inventory. Especially, high spatial and temporal resolution satellite images are easily accessed presently. An event landslide inventory is good for event-based susceptibility analysis and is feasible in construction of the inventory. Especially, high spatial and temporal resolution satellite images are easily accessed presently.

28 Thanks for your attention!