The land is a-moving in New Zealand

Huge fault rupture stretches 34km offshore from Kaikoura

The Kekerengu Fault ruptured for 36km on land and a further 34km in its offshore continuation the Needles Fault.

Stuff,

22 November, 2016

Scientists have found a huge fault rupture stretching 34km offshore from Kaikoura following last week's magnitude-7.8 earthquake.

Surveying the seabed from Niwa's research ship Tangaroa, they found the rupture in the offshore continuation of the Kekerengu Fault, known as the Needles Fault.

Voyage leader and Niwa marine geologist Dr Philip Barnes said the length of the Kekerengu-Needles fault rupture may extend for about 70km – 36km on land and 34km under the sea.

Mapping and profiling confirmed the Needles Fault had ruptured, forming newly discovered scarps - where one side of the fault moves vertically relative to the other side - on the seafloor along the Marlborough coast south of Cape Campbell.

Where it was measured under the sea, the scarps were 1-2 metres high, which was consistent with the uplift being seen onshore, Barnes said.

Scientists collected 61 sediment cores, each about 5.5m long from sites on the continental margin between the Kaikoura coast and Poverty Bay that will provide evidence of submarine landslides.

The cores revealed the earthquake generated a huge turbidity current in the Hikurangi Trough, offshore from Marlborough and Wairarapa. A turbidity current is a rapidly moving underwater current comprising mud, sand, gravel and water. It eventually results in layers of sediment being deposited across the sea floor. These are known as turbidite.

"We detected a very recent turbidite about 10-20cm thick over a very large region, extending at least 300km from Kaikoura. It is still settling on the seabed from the water column and may not complete this process for some time," Barnes said.

The precise location of the underwater landslides that generated the turbidity current was not studied.

Tangaroa was doing seismological research on the Hikurangi subduction zone, off the North Island's East Coast, before it was diverted to study the Kaikoura earthquake. The Hikurangi research is part of a five-year programme to fill in gaps in understanding about the earthquake potential of the one.

This is coming....

Urgent warning to stay away from the Conway River over "imminent" danger of dam collapse 

Stuff,

22 November, 2016

A 40-metre high landslide dam is in "imminent danger of over-topping".

Canterbury Civil Defence issued an urgent warning for Towy River, a tributary of Conway River in north Canterbury, shortly after 5pm.

"People are urged to stay out of the river bed and well away from the Conway River," the warning said.

"There are serious concerns for safety and nobody should be in or near the river."

Over-topping could result in a rapid water level and debris downstream on the Conway River.

The dam was caused after a huge landslide blocked the Towy River following Monday's earthquake.

Initial estimates put the dam at 40 metres high, and on Monday the water level was 15 metres below the top of the dam.

At the time, Civil Defence said "once water crests the top of the dam the possibility of rapid failure significantly increases".

An even larger dam was created over the Hapuku River, where a 150-metre high dam could also "rapidly fail", spilling water from a new lake into the river.

Due to the earthquake sequence, there was a risk of landslides and slips into the majority of rivers in North Canterbury and Kaikoura.

"As a precaution it is strongly advised to keep away from all riverbeds in case there are any sudden releases of water," Canterbury Civil Defence said.

This report is from 17 November

Landslide creates dangerous dam on Hapuku River, New Zealand

https://watchers.news/2016/11/17/hapuku-river-landslide-dam-new-zealand/

New Zealand's Kaikoura earthquake of November 13 caused a large landslide over the Hapuku River, creating a 150-meter (492 feet) dam. There are fears it could 'rapidly fail' with the recent rains and Canterbury Civil Defence Group has advised people to stay away from the river.

"There is a 150 m high dam caused by the earthquakes which could rapidly fail spilling water and debris from the new 'lake' over (or through) the dam due to heavy rain and building pressure," Civil Defence said in a Facebook post yesterday.

"We strongly advise people to stay away from the riverbed, especially as the situation could change quickly with further earthquakes and / or rainfall."

New Zealand police and others are out identifying any campers and residents in the area and warning them to stay clear of the river and moving anyone on that is in harm’s way.

Environment Canterbury said water backed up behind the dam was 30 m (98 feet) lower than the crest.

"It appears stable in its current state, but once water crests the top of the dam the possibility of rapid failure significantly increases. We expect any flow from the breach will be entirely contained within the river terraces. People are strongly advised to stay out of the riverbed."

Hapuku River dam. Credit: Canterbury Civil Defence Group

The landslide was on a tributary of the Hapuku near Barretts Bivouac, the agency added

The latest estimates are that the current and forecast rainfall is nowhere near enough to fill the dam – at least 450 mm (17.71 inches) of rain would be required to do this. There has only been around 20 mm (0.78 inches) so far, with another 20 mm expected overnight," Civil Defence said today.

The overall stability of the dam cannot be confirmed as helicopter access was restricted by weather today and there is still a risk of further aftershocks.

GNS, NIWA and Environment Canterbury are working together to provide a more technical assessment of this dam and others in the region.

The situation will be re-assessed after the rainfall on November 17/18

Landslide creating dam on Hapuku River, New Zealand. Photo by Neil Protheroe

As a result of the current earthquake sequence, there is an ongoing risk of landslides/slips into the rivers in North Canterbury and Kaikoura, Environment Canterbury added.

"As a precaution it is strongly advised to keep away from all riverbeds in case there are any sudden releases of water."

Other river warnings from Environment Canterbury (as of November 17):

Kaikoura District

Kowhai River: We have identified several smaller slides on tributaries to the Kowhai. None causing any major concern at this stage.

Kahutara River: There is a landslide dam on Linton Creek, a tributary to the Kahutara. The probability of a rapid failure is considered low. Regardless, caution is advised in the Kahutara Riverbed.

Hurunui District

Conway River: Yesterday we assessed a large, relatively stable landslide dam that has breached on the Conway River near Ferniehurst. There is also a landslide dam in the Towy River, which is a tributary to the Conway River located approximately 5km above the Inland Road Bridge. Initial estimates are that the dam is 40 m (131 feet) high. Water is backed up behind it and is approximately 15 m (49 feet) lower than the dam crest. It appears stable in its current state, but once water crests the top of the dam the possibility of rapid failure significantly increases. We expect any flow from the breach will be entirely contained within the river terraces. People are strongly advised to stay out of the riverbed. The situation will be re-assessed after the predicted rainfall on November 17/18.

Leader River: there is a large landslide but it is considered low risk.

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