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What are Landslides in New Zealand?

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Presentation on theme: "What are Landslides in New Zealand?"— Presentation transcript:

1 What are Landslides in New Zealand?
ICL Landslide Teaching Tools　 PPT-tool (1) What are Landslides in New Zealand? Stuart Read GNS Science (Lower Hutt, New Zealand)

2 Presentation will: Introduce landslides
ICL Landslide Teaching Tools　 PPT-tool (2) Presentation will: Introduce landslides Outline landslide descriptive approaches Give overview of impacts including reference to parts of course framework

3 Landslides Are a major landscape forming process Definition
ICL Landslide Teaching Tools　 PPT-tool (3) Landslides Are a major landscape forming process Definition “The movement of a mass of rock, debris or earth down a slope” Cruden (1991) excludes subsidence, collapse, snow avalanches

4 Other definitions seen include: (ex web)
ICL Landslide Teaching Tools　 PPT-tool (4) Other definitions seen include: (ex web) “gravity-driven movement of a mass of soil or rock” “general term referring to any rapid downhill movement of rock and soil” “geological phenomenon which includes a wide range of ground movement” “general term covering a wide variety of mass movement landforms and processes” “the downward sliding of a relatively dry mass of earth and rock” (also called landslip) “type of ‘mass wasting’ which denotes any down slope movement of soil and rock under the direct influence of gravity”

5 Variety of shapes & sizes - from small (<10 m3)
ICL Landslide Teaching Tools　 PPT-tool (5) Variety of shapes & sizes - from small (<10 m3)

6 to very large (>106 m3) Major landscape forming process
ICL Landslide Teaching Tools　 PPT-tool (6) to very large (>106 m3) Major landscape forming process

7 Variation in landslide type from
ICL Landslide Teaching Tools　 PPT-tool (7) Variation in landslide type from Material source (rock, soil etc) Type of movement (slide, flow etc) plus rate of movement (fast, slow etc) moisture content (dry, moist, saturated) movement history (timing) NZ text books include Crozier (1986), Selby (1993)

8 Role in landscape development depends on
ICL Landslide Teaching Tools　 PPT-tool (8) Role in landscape development depends on Geological environment rock-type, soil-type, weathering topography (steep, shallow slopes) tectonic and climatic environment Movement history (first time, reactivation) Size and frequency of occurrence Major material transport method before carried away from slopes as sediment (e.g. by river)

9 Causes (triggers) of landslides
ICL Landslide Teaching Tools　 PPT-tool (9) Causes (triggers) of landslides Natural (time) Earthquakes (strong shaking) Rainfall (storm) Man’s activities (physical modification) Impact (hazard and risk) urban, infrastructure, rural

10 Landslide description
ICL Landslide Teaching Tools　 PPT-tool (10) Landslide description Largely through classification based on: material type type of movement e.g. rock fall, debris flow, complex Other descriptors rate of movement e.g. rapid, slow activity e.g. first-time, reactivated, dormant

11 Landslide classification
ICL Landslide Teaching Tools　 PPT-tool (11) Landslide classification Classifications largely derived from transportation sector

12 Classification - a) ICL Landslide Teaching Tools
PPT-tool (12) Classification - a)

13 Classification - b) after Varnes (1978) ICL Landslide Teaching Tools
PPT-tool (13) Classification - b) after Varnes (1978)

14 Rate of movement (also part proxy for distance)
ICL Landslide Teaching Tools　 PPT-tool (14) Rate of movement (also part proxy for distance)

15 Landslide features ICL Landslide Teaching Tools
PPT-tool (15) Landslide features Complex (earth slide – earth flow)

16 ICL Landslide Teaching Tools　
PPT-tool (16) Examples:

17 ICL Landslide Teaching Tools　
PPT-tool (17) Examples: (cont)

18 Some issues Debris flows vs debris floods
ICL Landslide Teaching Tools　 PPT-tool (18) Some issues Debris flows vs debris floods Ground conditions (natural, regolith, man-made) Definition in legislation (landslide vs landslip) Other types (lahars - volcanic debris flows) In New Zealand legislation a debris flow is a landslide

19 Debris flows vs debris floods
ICL Landslide Teaching Tools　 PPT-tool (19) Debris flows vs debris floods transport method (at time and after)

20 Ground conditions Natural ground, man-made, regolith
ICL Landslide Teaching Tools　 PPT-tool (20) Ground conditions Natural ground, man-made, regolith

21 Landslide in legislation
ICL Landslide Teaching Tools　 PPT-tool (21) Landslide in legislation Resource Management Act (1991) “Natural hazard” any atmospheric or earth or water related occurrence (including earthquake, tsunami, erosion, volcanic and geothermal activity, landslip, subsidence, sedimentation, wind, drought, fire, or flooding) the action of which adversely affects or may adversely affect human life, property, or other aspects of the environment: Earthquake Commission Act (1993) “Natural landslip” ... movement (whether by way of falling, sliding, or flowing, or by a combination thereof) of ground-forming materials composed of natural rock, soil, artificial fill, or a combination of such materials, which, before movement, formed an integral part of the ground; but does not include the movement of ground due to below-ground subsidence, soil expansion, soil shrinkage, soil compaction, or erosion:

22 Landslide in legislation (cont)
ICL Landslide Teaching Tools　 PPT-tool (22) Landslide in legislation (cont) Building Act (2004) “Natural hazard” any of erosion (including coastal erosion, bank erosion, and sheet erosion): (b) falling debris (including soil, rock, snow, and ice): (c) subsidence: (d) inundation (including flooding, overland flow, storm surge, tidal effects, and ponding): slippage. Note that the word “landslide” does not appear in any New Zealand legislation

23 2007 Ruapehu lahar ICL Landslide Teaching Tools
PPT-tool (23) Ruapehu lahar

24 Impact (hazard and risk)
ICL Landslide Teaching Tools　 PPT-tool (24) Impact (hazard and risk) Effects may be housing, infrastructural, rural may be positive (provide buttress) more often negative (raised water table, reactivation potential) Indicators of occurrence more prone areas (geology, slope) trigger effects (rainfall, earthquakes) vegetation change (removal) physical change (slope surcharge or toe removal)

25 ICL Landslide Teaching Tools　
PPT-tool (25) Housing examples

26 Many houses on large slide
ICL Landslide Teaching Tools　 PPT-tool (26) Many houses on large slide

27 Infrastructure examples
ICL Landslide Teaching Tools　 PPT-tool (27) Infrastructure examples

28 ICL Landslide Teaching Tools　
PPT-tool (28) Rural examples

29 ICL Landslide Teaching Tools　
PPT-tool (29) Remote examples

30 ICL Landslide Teaching Tools　
PPT-tool (30) The hand of man

31 Hazard reduction and avoidance
ICL Landslide Teaching Tools　 PPT-tool (31) Hazard reduction and avoidance Hazard and risk hazard identification and assessment Topographic maps Vertical aerial photos (orthophotos) Ground examination risk assessment, susceptibility Hazard reduction awareness acceptance mitigation (avoidance, impact limitation)

32 Sleuthing the signs ICL Landslide Teaching Tools
PPT-tool (32) Sleuthing the signs

33 Defining the model ICL Landslide Teaching Tools
PPT-tool (33) Defining the model

34 Implementing solutions
ICL Landslide Teaching Tools　 PPT-tool (34) Implementing solutions

35 Being at the coal face is not easy
ICL Landslide Teaching Tools　 PPT-tool (35) Being at the coal face is not easy

36 Concluding remarks Landslides: are widespread throughout New Zealand
ICL Landslide Teaching Tools　 PPT-tool (36) Concluding remarks Landslides: are widespread throughout New Zealand come in a wide range of sizes have a variety of movement styles are caused by a number of triggering factors are a fundamental landscape forming process can have a significant impact on society

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