Sunday, April 18, 2010
Worrying signs on the landslide at Attabad in Hunza
The water level at the landslide dam at Attabad in Pakistan continues to rise (see the data on my Hunza landslide monitoring site), with the reported freeboard being less than 30 metres. However, I have to report a very much more worrying development. Dr Michele Comi and Dr Chiara Calligaris from Ev-K2-CNR are just returning from a visit to the site, and have sent me the picture below (reproduced with permission):
This sinkhole has apparently opened up on the upstream side of the dam. The most likely cause of a sinkhole is that erosion is occurring in the core of the dam, although this could be localised. However, given that seepage is now accelerating again, the signs are worrying.
Saturday, April 17, 2010
Extraordinary video of a Jokulhlaup in Iceland
A jokulhlaup is a sudden release of water from beneath a glacier. One of the key triggers for Jokulhlaup is the eruption of a volcanic beneath an icecap. It shouldn't be a surprise to hear that jokulhlaups have been triggered by the Eyjafjallajokull eruption that is causing such chaos across Europe (guess who was supposed to go to Hong Kong on Thursday...), and increasingly beyond.
Now, a jokulhlaup is not technically a landslide, but as these flood carry vast amounts of debris they are at the hyper-concentrated flow / debris flow end of the flood spectrum. On that basis I thought it reasonable to show this fantastic video of a jokulhlaup cascading off the margins of the Eyjafjallajokull volcano on 14th April 2010:
Incredible!
Now, a jokulhlaup is not technically a landslide, but as these flood carry vast amounts of debris they are at the hyper-concentrated flow / debris flow end of the flood spectrum. On that basis I thought it reasonable to show this fantastic video of a jokulhlaup cascading off the margins of the Eyjafjallajokull volcano on 14th April 2010:
Incredible!
Friday, April 16, 2010
Latest update on the Hunza (Attabad) landslide in Pakistan
I have today updated my monitoring site for the Hunza (Attabad) landslide. However, there are a number of key developments that are worth noting:
1. The rate of seepage has started to increase once again
The graph of seepage against time shows that seepage is increasing rapidly at the moment, albeit at rates that are still only a fraction of the inflow rate:
The key factor here is the development of a new seepage point on the dam face (seepage point 4), which is now producing about 85 litres per second of water. The location of the four seepage points are shown below (from Focus):
Seepage points 2 and 3 cause me little concern given their location. Points 1 and 4 are clearly the ones that probably represent seepage from the lake.
2. The date of overtopping remains unclear
The outgoing NDMA chair recently estimated that overtopping could occur on 17th April (i.e. tomorrow). This is highly unlikely. On the monitoring site I try to estimate the date of overtopping based on the reported rate of reduction of the freeboard. My current best estimate is mid-June. However, the lake length has not really been increasing recently as the upstream section is currently steep (see image below from the Pamir Times:
Once this steep section is overcome the rate of rise may decline. However, this may be offset by an increase in inflow as snowmelt develops.
3. Something strange is reported at Shishkat
Shishkat is near the head of the lake, probably best known for the location of the KKH bridge that has now been drowned (image from the Pamir Times):
Local people at Shiskat are reporting "underground blast-like sounds" in this area. Of course there is little information about what these "blasts" might be, or indeed the reliability of the reports. However, one possibility would be the development of slope instability on the banks of the lake. Given that one failure mechanism for the dam is a slide into the lake and a wave that then overtops the dam, this needs to be checked out with some urgency.
1. The rate of seepage has started to increase once again
The graph of seepage against time shows that seepage is increasing rapidly at the moment, albeit at rates that are still only a fraction of the inflow rate:
The key factor here is the development of a new seepage point on the dam face (seepage point 4), which is now producing about 85 litres per second of water. The location of the four seepage points are shown below (from Focus):
Seepage points 2 and 3 cause me little concern given their location. Points 1 and 4 are clearly the ones that probably represent seepage from the lake.
2. The date of overtopping remains unclear
The outgoing NDMA chair recently estimated that overtopping could occur on 17th April (i.e. tomorrow). This is highly unlikely. On the monitoring site I try to estimate the date of overtopping based on the reported rate of reduction of the freeboard. My current best estimate is mid-June. However, the lake length has not really been increasing recently as the upstream section is currently steep (see image below from the Pamir Times:
Once this steep section is overcome the rate of rise may decline. However, this may be offset by an increase in inflow as snowmelt develops.
3. Something strange is reported at Shishkat
Shishkat is near the head of the lake, probably best known for the location of the KKH bridge that has now been drowned (image from the Pamir Times):
Local people at Shiskat are reporting "underground blast-like sounds" in this area. Of course there is little information about what these "blasts" might be, or indeed the reliability of the reports. However, one possibility would be the development of slope instability on the banks of the lake. Given that one failure mechanism for the dam is a slide into the lake and a wave that then overtops the dam, this needs to be checked out with some urgency.
Wednesday, April 14, 2010
First news of the Qinghai Earthquake in China
This morning's Mw=6.9 earthquake in China is now reported to have killed at least 300 people, with the toll likely to rise over the next few hours. Although the earthquake occurred in an area with a low population total and density, vulnerability of both buildings and the landscape to shaking is likely to be high, especially given the reported shallow nature (depth = 10 km) of the event.
The Google Earth imagery of the area shows a landscape that is sparsely populated with substantial mountains such that landslides may well be a serious issue.
The landscape appears to vary, with rolling hills in the south (image from here):
To the north the landscape is undoubtedly steeper and more rugged, and thus landslide-prone: (image from here)
The town in the foreground above is Jiegu (sometimes spelt Gyegu). Early reports suggest that up to 80% of the buildings in the town have been destroyed. Images of the town before the earthquake suggest that it is likely to have been very vulnerable both to ground shaking and to landslides:
Given the remoteness of this area, and the likelihood of landslides on the roads, the delivery of aid is going to be a major challenge. My earlier comments on the reporting of large earthquakes in mountain areas applies here once again (insert China for Haiti):
1. Everything stops at night. At the time of writing it is still night time on Haiti. In the aftermath of an earthquake electricity and power supplies are wiped out, so for the night time period it appears that the disaster is not as bad as is feared. As the sun comes up so the reports on the true picture start to emerge, and the fatality statistics start to increase rapidly. This increase will continue for several days at least, but may ultimately exceed the final toll;
2. The initial focus is often wrong. In the immediate aftermath of a disaster the initial focus of the media reports is often on the biggest city. This is rarely where the biggest impact has occurred, but it is most accessible so will be the focus of the reports.
3. No news is very, very bad news. The biggest impacts are often in rural areas with the highest levels of shaking. These areas had poor communications to start with, but when an earthquake strikes the roads become blocked, power is lost and there is no telephone service. Therefore, no news comes out for some time after the quake. The picture is actually the opposite of the obvious. If news starts to emerge quickly from those areas with the highest shaking then the picture is not as bad as we feared - at least some communications are open - although it may still be quite grim. If there is almost no news at all from the rural areas for a day or two, then the picture is probably very bad indeed, with almost all of the communications wiped out.
4. The media focus will quickly change to the foreign rescue teams. However, although these efforts are valuable, their overall impact is very small. The real work is actually done by local people - most rescues are made by untrained people in the first 24 hours - this should really be the focus.
The Google Earth imagery of the area shows a landscape that is sparsely populated with substantial mountains such that landslides may well be a serious issue.
The landscape appears to vary, with rolling hills in the south (image from here):
To the north the landscape is undoubtedly steeper and more rugged, and thus landslide-prone: (image from here)
The town in the foreground above is Jiegu (sometimes spelt Gyegu). Early reports suggest that up to 80% of the buildings in the town have been destroyed. Images of the town before the earthquake suggest that it is likely to have been very vulnerable both to ground shaking and to landslides:
Given the remoteness of this area, and the likelihood of landslides on the roads, the delivery of aid is going to be a major challenge. My earlier comments on the reporting of large earthquakes in mountain areas applies here once again (insert China for Haiti):
1. Everything stops at night. At the time of writing it is still night time on Haiti. In the aftermath of an earthquake electricity and power supplies are wiped out, so for the night time period it appears that the disaster is not as bad as is feared. As the sun comes up so the reports on the true picture start to emerge, and the fatality statistics start to increase rapidly. This increase will continue for several days at least, but may ultimately exceed the final toll;
2. The initial focus is often wrong. In the immediate aftermath of a disaster the initial focus of the media reports is often on the biggest city. This is rarely where the biggest impact has occurred, but it is most accessible so will be the focus of the reports.
3. No news is very, very bad news. The biggest impacts are often in rural areas with the highest levels of shaking. These areas had poor communications to start with, but when an earthquake strikes the roads become blocked, power is lost and there is no telephone service. Therefore, no news comes out for some time after the quake. The picture is actually the opposite of the obvious. If news starts to emerge quickly from those areas with the highest shaking then the picture is not as bad as we feared - at least some communications are open - although it may still be quite grim. If there is almost no news at all from the rural areas for a day or two, then the picture is probably very bad indeed, with almost all of the communications wiped out.
4. The media focus will quickly change to the foreign rescue teams. However, although these efforts are valuable, their overall impact is very small. The real work is actually done by local people - most rescues are made by untrained people in the first 24 hours - this should really be the focus.
Tuesday, April 13, 2010
Junk natural hazards science of the month - earthquake risks to the World Cup in South Africa
Although this is meant to be a blog on landslides, occasionally things appear in other areas of natural hazards that are so irritatingly ridiculous that I just can't let them go. And so in the last few days a story has been doing the rounds about earthquake risk to the forthcoming football World Cup in South Africa. For example, The Daily Star newspaper in the UK (not necessarily worth reading on a normal day) is carrying the story:
There are some extraordinary quotes, from the source of the story, Dr Chris Hartnady:
"A major earthquake disaster in the region is inevitable because wide areas of southern Africa are affected by the slow, southward spread of the East African rift system...It is not a question of if, but when. The consequences would be so expensive in terms of mortality and economic cost that the risk of being ill-prepared is unacceptably high.”
So lets take a look at the seismic record for South Africa. First, here is the USGS seismic hazard map for Africa:
Whilst the seismic hazard for South Africa is not zero, it is comparatively low. For comparison, here is the similar map for Europe:
You will see that South Africa's seismic hazard is similar to, and in many cases lower than, that of the UK. Hardly a major source of concern. Here is a map of earthquakes since 1990, again from the USGS:
Compare the number of recorded events in the Mediterranean area (top of the image) with that of South Africa to get an idea of the level of hazard in the latter.
Of course an earthquake can in theory happen anywhere and of course if the community is unprepared then the impacts of said event can be devastating. However, the level of seismic hazard in South Africa is not high, and the likelihood of a large earthquake there during the four weeks of the World Cup is vanishingly small.
Of greater concern is how any team can hope to cope with Argentina's maestro Lionel Messi!
There are some extraordinary quotes, from the source of the story, Dr Chris Hartnady:
"A major earthquake disaster in the region is inevitable because wide areas of southern Africa are affected by the slow, southward spread of the East African rift system...It is not a question of if, but when. The consequences would be so expensive in terms of mortality and economic cost that the risk of being ill-prepared is unacceptably high.”
So lets take a look at the seismic record for South Africa. First, here is the USGS seismic hazard map for Africa:
Whilst the seismic hazard for South Africa is not zero, it is comparatively low. For comparison, here is the similar map for Europe:
You will see that South Africa's seismic hazard is similar to, and in many cases lower than, that of the UK. Hardly a major source of concern. Here is a map of earthquakes since 1990, again from the USGS:
Compare the number of recorded events in the Mediterranean area (top of the image) with that of South Africa to get an idea of the level of hazard in the latter.
Of course an earthquake can in theory happen anywhere and of course if the community is unprepared then the impacts of said event can be devastating. However, the level of seismic hazard in South Africa is not high, and the likelihood of a large earthquake there during the four weeks of the World Cup is vanishingly small.
Of greater concern is how any team can hope to cope with Argentina's maestro Lionel Messi!
Monday, April 12, 2010
Toyota Yaris vs rock...
The Mirror newspaper in the UK yesterday carried a dramatc illustration of the effect that a boulder can have on a car. This car was parked by the side of the road in Hayfield in Derbyshire on Sunday when an eight tonne boulder slipped off a lorry. Fortunately there was no-one in the car:
Time to buy a new bottle of T-cut? Picture from the Mirror
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