The Young River landslide Chris Massey, Mauri McSaveney, … · 2015-10-25 · The North Branch of...
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GNS Science Location Young River Landslide, North Branch Young River (Mount Aspiring National Park), New Zealand, which is a tributary of the Makarora River. Initiation Date/time 04:40 on 29 August 2007 Trigger No obvious trigger (no rainfall three weeks prior to initiation and no earthquakes recorded) Landslide Volume 11 Million m 3 Velocity 100 km/hour (minimum) Runout distance 1.8 km Impounded Lake Volume 23 Million m 3 Dam height (at outflow channel) 70 m 16:40 25”, 28 August, 2007 (UT) 0 100 200 300 400 500 600 700 800 1-Aug-07 31-Aug-07 30-Sep-07 30-Oct-07 Date Cummulative Rainfall (mm) Makarora Rainfall at Makarora Telemetry Albert Burn Rainfall at Dragon Fly Landslide dam overtopped Landslide dam formed Data from Otago Regional Council The North Branch of the Young River, near Lake Wanaka, New Zealand, at 4:40 am on 29 August 2007. The debris avalanche occurred in closely jointed schist, forming a dam 70 m high across the valley. Water began impounding behind the dam and has now overtopped, scouring an outflow channel on the downstream face of the dam. was blocked by a large landslide immediately 578.5 579.7 580.8 582.0 3-Nov-07 18-Nov-07 3-Dec-07 18-Dec-07 2-Jan-08 17-Jan-08 1-Feb-08 16-Feb-08 2-Mar-08 17-Mar-08 1-Apr-08 Date Lake Level (m above mean sea level) Assumed lowest point of dam crest November 2007 579.7 m Assumed lowest point of dam crest April 2008 579.4 m Young River The Young River landslide is in a remote headwater tributary of the Makarora River and was first recognised by a helicopter pilot three weeks after initiation. Seismic shaking generated by the landslide was the equivalent of a magnitude 2.9 earthquake, and was recorded by the GeoNet seismic network. Debris from the landslide travelled approximately 1.8 kilometres in 60 seconds, suggesting a minimum debris speed of 100km/hour. The source of the avalanche was located on what is locally referred to as Haunted Spur, above the river's true right bank. The main scarp is at an elevation of 1600 m, with an elevation difference (between the top of the source area and toe of the debris) of 1100 meters. Several terrestrial laser scans (TLS) of the landslide dam (deposit) and source area (using a RIEGL LMS-Z420i scanner) have been carried out. These data have been used to generate a three-dimensional model of the landslide deposit. This model has been compared with the pre- failure topography, to calculate the landslide and lake volumes. This information has been used by both GNS scientists and emergency management officers at the Otago Regional Council and has provided essential information for assessing its future stability as a dam. The dam is about 70 metres high at the outflow and the impounded lake is approximately two kilometres in length and 500 metres at its widest point. Water overtopped the dam on Friday 5 October, approximately 5 weeks after its formation. Water continues to flow over the dam crest and has scoured material from along the outflow channel after periods of high rainfall and associated outflows. Equipment to remotely monitor the lake level has been installed . Rapid dam failure during high outflows remains possible. The maximum outbreak flow rate for such a failure could be as high as 3500 m s- (estimated from Costa/Schuster empirical relationship). Any flood wave would attenuate as it moves down the Young valley to the Makarora confluence. Given this the Department of Conservation have closed access to the lower Young River to ensure public safety, and the Otago Regional Council is monitoring the situation to manage the safety of people in the Makarora Valley. GNS Science is providing information gathered from our monitoring to both Department of Conservation and the Otago Regional Council. Failures associated with overtopping are more likely to occur during periods of heavy rain when lake discharge flows will be added to high flood flows in the Young and perhaps in the Makarora Rivers. Unusual water surface elevations and sediment deposition may occur in the Makarora River as a result, both upstream and downstream of the confluence. It is likely that the Makarora River will be deflected east at the Young confluence if a flood were to occur. However, it is also possible the dam and lake could be part of the landscape for a long time. 3 1 Using a tripod-mounted laser scanner, geologist Chris Massey and surveyor Neville Palmer, both of GNS Science, have measured the volume of the landslide at 11 million cubic meters. These images show the 3D model before, and after the landslide. 0 500 1000 1500 0 500 1000 1500 2000 note: The pre-failure topography is derived from 1:50,000 Topographic map WILKIN F38. Post failure topography is based on data from Terrestrial laser scan surveys. Haunted Spur (1680m amsl) Main scarp Source area ROCK AVALANCHE TRAVEL PATH approx. profile of present slope (failure surface) North branch of Young River Former level of river channel (480m amsl) Schist Tension cracks Overtop channel (580m) Landslide dam (m) (m) approx. profile of pre-failure slope Acknowledgements: Gavin Palmer (Otago Regional Council), Paul Hellebrekers (Department of Conservation), Tim Davies (Canterbury University), Oliver Korup (Swiss Federal Institute for Snow andAvalanche Research) 500 m View of landslide and dam looking north west. Engineering geological map of the landslide. Cross section of Young River debris avalanche and landslide dam Young River area rainfall data. Young River lake level monitoring data. Seismic trace generated by the landslide. View of landslide debris forming dam, looking north west. Solar panels provide power to lake level monitoring instrumentation and communication equipment. The Young River landslide Mauri McSaveney, Neville Palmer, Vern Manville & Graham Hancox Chris Massey, Introduction Summary of Key Facts Discussion
Transcript of The Young River landslide Chris Massey, Mauri McSaveney, … · 2015-10-25 · The North Branch of...
GNS Science
Location Young River Landslide, North Branch Young River(Mount Aspiring National Park), New Zealand, whichis a tributary of the Makarora River.
Initiation Date/time 04:40 on 29 August 2007
Trigger No obvious trigger (no rainfall three weeks prior toinitiation and no earthquakes recorded)
Landslide Volume 11 Million m3
Velocity 100 km/hour (minimum)
Runout distance 1.8 km
Impounded Lake Volume 23 Million m3
Dam height (at outflow channel) 70 m
16:40 25”,
28 August,
2007 (UT)
0
100
200
300
400
500
600
700
800
1-Aug-07 31-Aug-07 30-Sep-07 30-Oct-07
Date
Cu
mm
ula
tiv
eR
ain
fall
(mm
) Makarora Rainfall at
Makarora Telemetry
Albert Burn Rainfall
at Dragon Fly
Landslide damovertopped
Landslide dam formed
Data from Otago Regional Council
The North Branch of the Young River, near
Lake Wanaka, New Zealand,
at 4:40 am on 29
August 2007. The debris avalanche
occurred in closely jointed schist,
forming a dam 70 m high across
the valley. Water
began impounding behind
the dam and has now
overtopped, scouring an
outflow channel on the
downstream face of the
dam.
was blocked
by a large landslide
immediately
578.5
579.7
580.8
582.0
3-Nov-07 18-Nov-07 3-Dec-07 18-Dec-07 2-Jan-08 17-Jan-08 1-Feb-08 16-Feb-08 2-Mar-08 17-Mar-08 1-Apr-08
Date
Lake
Level(m
ab
ove
mean
sea
level)
Assumed
lowest point of
dam crest
November
2007 579.7 m
Assumed lowest point of dam
crest April 2008 579.4 m
YoungRiver
The Young River landslide is in a remote headwater tributary of theMakarora River and was first recognised by a helicopter pilot threeweeks after initiation. Seismic shaking generated by the landslide wasthe equivalent of a magnitude 2.9 earthquake, and was recorded bythe GeoNet seismic network. Debris from the landslide travelledapproximately 1.8 kilometres in 60 seconds, suggesting a minimumdebris speed of 100km/hour.
The source of the avalanche was located on what is locally referred toas Haunted Spur, above the river's true right bank. The main scarp isat an elevation of 1600 m, with an elevation difference (between thetop of the source area and toe of the debris) of 1100 meters. Severalterrestrial laser scans (TLS) of the landslide dam (deposit) and sourcearea (using a RIEGL LMS-Z420i scanner) have been carried out.These data have been used to generate a three-dimensional model ofthe landslide deposit. This model has been compared with the pre-failure topography, to calculate the landslide and lake volumes. Thisinformation has been used by both GNS scientists and emergencymanagement officers at the Otago Regional Council and has providedessential information for assessing its future stability as a dam.
The dam is about 70 metres high at the outflow and the impoundedlake is approximately two kilometres in length and 500 metres at itswidest point. Water overtopped the dam on Friday 5 October,approximately 5 weeks after its formation. Water continues to flowover the dam crest and has scoured material from along the outflowchannel after periods of high rainfall and associated outflows.Equipment to remotely monitor the lake level has been installed .
Rapid dam failure during high outflows remains possible. Themaximum outbreak flow rate for such a failure could be as high as3500 m s- (estimated from Costa/Schuster empirical relationship).Any flood wave would attenuate as it moves down the Young valley tothe Makarora confluence. Given this the Department of Conservationhave closed access to the lower Young River to ensure public safety,and the Otago Regional Council is monitoring the situation to managethe safety of people in the Makarora Valley. GNS Science is providinginformation gathered from our monitoring to both Department ofConservation and the Otago Regional Council.
Failures associated with overtopping are more likely to occur duringperiods of heavy rain when lake discharge flows will be added to highflood flows in the Young and perhaps in the Makarora Rivers. Unusualwater surface elevations and sediment deposition may occur in theMakarora River as a result, both upstream and downstream of theconfluence. It is likely that the Makarora River will be deflected east atthe Young confluence if a flood were to occur. However, it is alsopossible the dam and lake could be part of the landscape for a longtime.
3 1
Using a tripod-mounted laser scanner, geologist ChrisMassey and surveyor Neville Palmer, both of GNS Science,have measured the volume of the landslide at 11 million cubicmeters.
These images show the 3D model before, and after thelandslide.
0
500
1000
1500
0 500 1000 1500 2000
note: The pre-failure topography is derived from 1:50,000 Topographic map WILKIN F38.Post failure topography is based on data from Terrestrial laser scan surveys.
Haunted Spur (1680m amsl)
Main scarp
Source area
ROCK
AVALANCHETRAVEL
PATH
approx. profile ofpresent slope(failure surface)
North branchof Young River
Former level of riverchannel (480m amsl)
Schist
Tensioncracks
Overtopchannel(580m)
Landslidedam
(m)
(m)
approx. profile ofpre-failure slope
Acknowledgements:Gavin Palmer (Otago Regional Council), Paul Hellebrekers (Department of Conservation), Tim Davies (Canterbury University), Oliver Korup (Swiss Federal Institute for Snow andAvalanche Research)
500 m
View of landslide and dam looking north west.
Engineering geological map of the landslide.
Cross section of Young River debris avalanche and landslide dam
Young River area rainfall data.
Young River lake level monitoring data.
Seismic trace generated by the landslide.
View of landslide debris forming dam, looking north west.
Solar panels provide power to lake level monitoring instrumentation and communicationequipment.
The Young River landslide
Mauri McSaveney, Neville Palmer, Vern Manville & Graham HancoxChris Massey,
Introduction
Summary of Key Facts
Discussion
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