Landslide Mapping And Construction of a Landslide Inventory

Landslide Mapping And Construction of a Landslide Inventory Chyi-Tyi Lee Graduate Institute of Applied Geology, National Central University, Taiwan 2014暑期坡地營課程 06/08/2014 1

Introduction l 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. ) l Types of mass-movement: Gradual mass-movement Creeping slope Rapid mass-movement Landslide – any large, fast mass-movement 2

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

Classification of Landslide Type of material Type of movement Bedrock Engineering soils Fine Coarse Rockfall Earth fall Debris fall Topples Rock topple Earth topple Debris topple Rock slump Earth slump Debris slump Few units Rock block slide Earth block slide Debris block slide Many units Rock slide Earth slide Debris slide Rock spread Earth spread Debris spread Rock flow Earth flow Debris flow Slides Falls Rotational Translational Lateral spreads Flows Rock avalanche (Deep creep) Complex and compound Debris avalanche (Soil creep) Combination in time and/or space of two or more principal types of movement Classification of Varnes 1978 and taking into account the modifications made by Cruden and Varnes, in 1996. Some integration have been made by using the definitions of Hutchinson (1988) and Hungr et al. 2001. 4

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

Triggering Mechanism of Landslide Physical Causes ● ● 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 Human Causes ● Excavation Loading Draw-down Water management Mining Quarrying Vibration Water leakage Deforestation Land use pattern Pollution Adopted from: http: //en. wikipedia. org/wiki/Causes_of_landslides 6

Preparation Works for Mapping of Landslides (1/2 ) l 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. l 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. l 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. 7

Preparation Works for Mapping of Landslides (2/2 ) l 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. l Enhancement of an Image (1) (2) (3) (4) Linear stretching Gamma correction Proper saturation Sharpening a little bit l Registration of an Image Registration of an image in a GIS system using the image coordinates and projection. 8

SPOT Images for Mapping Landslides induced by the Typhoon Aere Event Pre-event 20040210 Post-event 20041102 9

Recognition of Landslides on Remote Sensing Image l 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. 10

Landslide (area 1. 8 ha. ) SPOT 5 image for extraction of landslides 11

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

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

Lab Checks of Landslide Inventory l Checks If a Landslide Covers a Ridge Line (2/2 ) Ø 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, landslides or it may be a big landslide. l Checks If a Landslide Covers a Stream Channel Ø 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, landslides or it may be a landslide dam. 15

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

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

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

Pre-Chi. Chi EQ landslides Example of Building an Event Landslide Inventory by Method 1 (Kuohsing Quadrangle) Post-Chi. Chi EQ landslides Chi-Chi EQinduced landslides 5, 496 slides, totaling 22. 06 km 2 19

Event Landslide Inventory – Method 1 Case 2 Case 3 20

Event Landslide Inventory – Method 1 Pre-event 事件前 Post-event 事件後 New 新增 Landslide Enlarged Landslide 擴大 No 刷深 Change Others 其它

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

Event Landslide Inventory – Method 2 1 2 2 3 New Landslide 1 3 New Landslide 4 4 Enlarged Landslide

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

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

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

Usage of a Landslide Inventory l Single-period landslide inventory for susceptibility analysis may be biased in building a model. l 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. l 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. 27

Thanks for your attention! 28 28