ERLAWS
Encyclopedia
Lahar
A lahar is a type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris, and water. The material flows down from a volcano, typically along a river valley. The term is a shortened version of "berlahar" which originated in the Javanese language of...
warning system installed on Mount Ruapehu
Mount Ruapehu
Mount Ruapehu, or just Ruapehu, is an active stratovolcano at the southern end of the Taupo Volcanic Zone in New Zealand. It is 23 kilometres northeast of Ohakune and 40 kilometres southwest of the southern shore of Lake Taupo, within Tongariro National Park...
, New Zealand, following volcanic eruption
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...
s in 1995–1996. The system successfully detected and warned about a lahar in March 2007. The system is being expanded to detect the wider range of lahar threats now expected on Ruapehu.
Introduction
The 1995–1996 eruptions of Ruapehu in the North IslandNorth Island
The North Island is one of the two main islands of New Zealand, separated from the much less populous South Island by Cook Strait. The island is in area, making it the world's 14th-largest island...
of New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
left a 7-metre high dam of tephra
Tephra
200px|thumb|right|Tephra horizons in south-central [[Iceland]]. The thick and light coloured layer at center of the photo is [[rhyolitic]] tephra from [[Hekla]]....
, consisting of volcanic ash
Volcanic ash
Volcanic ash consists of small tephra, which are bits of pulverized rock and glass created by volcanic eruptions, less than in diameter. There are three mechanisms of volcanic ash formation: gas release under decompression causing magmatic eruptions; thermal contraction from chilling on contact...
and rock, around the rim of the crater lake
Crater lake
A crater lake is a lake that forms in a volcanic crater or caldera, such as a maar; less commonly and with lower association to the term a lake may form in an impact crater caused by a meteorite. Sometimes lakes which form inside calderas are called caldera lakes, but often this distinction is not...
.
It was realised that some time after the lake refilled and rose above the level of its normal outlet, the tephra dam would collapse, causing a large lahar
Lahar
A lahar is a type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris, and water. The material flows down from a volcano, typically along a river valley. The term is a shortened version of "berlahar" which originated in the Javanese language of...
. Such a lahar resulted in the 1953 Tangiwai disaster
Tangiwai disaster
The Tangiwai disaster on 24 December 1953 was the worst rail accident in New Zealand history. An 11-carriage overnight express from Wellington to Auckland fell into the Whangaehu River at Tangiwai, ten kilometres west of Waiouru. The bridge carrying the North Island Main Trunk Railway over the...
when 151 people lost their lives as the lahar swept the railway bridge away, causing a passenger train to plunge into the Whangaehu River
Whangaehu River
The Whangaehu River is a large river in central North Island of New Zealand. Its headwaters are the crater lake of Mount Ruapehu on the central plateau, and it flows into the Tasman Sea eight kilometres southeast of Wanganui.-Length:...
.
In 2000 the government decided to plan, design and implement ERLAWS - a complex system of sensors and preventative mechanisms to warn of an impending lahar.
Sensors
ERLAWS consists of 3 sites at which various sensors are located - these are:- Site 1 (Crater Lake outlet)
- three geophones to detect the vibration of the collapse and from lahars
- a buried tripwire to detect collapse of the dam
- water level sensors to detect a sudden drop in lake level
- Site 2 (NZ Alpine Club hut)
- two geophones to detect the vibration from passing lahars
- Site 3 (near Tukino skifield)
- two geophones to detect the vibration from passing lahars.
Monitoring
Signals from the sites are transmitted to the Genesis Power power station at TokaanuTokaanu
Tokaanu is a small settlement close to Turangi at the southern end of Lake Taupo. The Tokaanu Thermal Pools and the easy access to Lake Taupo make it a popular lakeside holiday destination. A short walking track through the Tokaanu thermal area leads past steaming hot mineral pools and small mud...
, where computers monitor the data received (via GE Fanuc's Proficy iFIX SCADA HMI) and upload it to an external server and the ERLAWS website.
When incoming data meets or exceeds pre-set thresholds alarms are sent via pagers (powered by Win-911 from Specter Instruments) to police, district council staff, Transit New Zealand
Transit New Zealand
Transit New Zealand was, from 1989 to 2008, the New Zealand Crown entity responsible for operating and planning the New Zealand State Highway network...
, ONTRACK
OnTrack
OnTrack was a regional rail line that operated in Syracuse, New York from 1994 to 2007. During its operation, Syracuse was the smallest city in the United States to have regional train service. The line ran from Colvin Street on the city's south side via Syracuse University and Armory Square to the...
and duty scientists who will then respond following predetermined plans. This alert can be up to two hours before a lahar would reach Tangiwai.
Transit systems
Transit New ZealandTransit New Zealand
Transit New Zealand was, from 1989 to 2008, the New Zealand Crown entity responsible for operating and planning the New Zealand State Highway network...
has systems installed on the State Highway
State highway
State highway, state road or state route can refer to one of three related concepts, two of them related to a state or provincial government in a country that is divided into states or provinces :#A...
s surrounding the area, which alert motorists and in some cases prevent entry to the danger areas. These systems incorporate automatic barrier gates, flashing lights and electronic signs warning of flash flooding.
Events
On March 18, 2007, the tephraTephra
200px|thumb|right|Tephra horizons in south-central [[Iceland]]. The thick and light coloured layer at center of the photo is [[rhyolitic]] tephra from [[Hekla]]....
dam collapsed, causing a "medium" sized lahar which flowed down the mountain and into the Whangaehu River. The ERLAWS system activated at 10:47am and worked exactly as planned. Scientists estimate that 1.29 million cubic metres (1.29 billion litres) of sulphur and water went down the Whangaehu Valley, leaving 8.9 million cubic meters in the crater lake. This lahar was at least 50% larger than the 1953 lahar that caused the Tangiwai disaster.