Remarkable NASA imagery of catastrophic flooding around Manchhar Lake in Pakistan

NASA have provided the most dramatic evidence yet of the catastrophic floods that are occurring around Manchhar (Manchar) Lake in Pakistan (see my post yesterday on this issue).  This image was captured by the ALI instrument on 18th September:

Compare this with an image taken of the same area just three days earlier:

Or the Google Earth image of the same area, which was collected in May this year:

Geo-TV, an independent TV station in Pakistan, reports that some of the breaches that are causing these floods are now 1 km wide, whilst NTDTV notes that the number of people displaced by this most recent component of the floods may be as high as 250,000. 


The breaches have allowed the water level in the main body of the lake to fall slightly, bringing some relief elsewhere, but with new areas continuing to experience flooding that is not cause for much overall cheer.

Zhouqu landslide - NASA satellite image

NASA have somehow managed to find a gap in the clouds to collect a satellite image of the Zhouqu landslide site.  Readers at the time of the landslide last month will remember that I was wondering about the source of the slides.  Although this image does not give a full answer, it gets us a part of the way there:

A zoom into the affected area yields this:

The slides (note the smaller one to the right of the main event) clearly originated as a series of smaller slips on the walls and headwaters of the upstream catchments.  These appear to have coalesced to form the main events.  This is consistent with processes observed elsewhere during periods of exceptional rainfall.

Meanwhile, I am now in Christchurch in New Zealand, site of the earthquake of 12 days ago.  Every 30 minutes or so my chair shakes as an aftershock rattles the area, which is a very surreal experience.

Earthquake-driven coastal erosion (or a coastal lateral spread) in Haiti

The Discovery Channel has news of a very interesting example of rapid coastal erosion driven by the earthquake in Haiti. The site is at Petit Paradis to the west of Port-au-Prince. Eye-witness reports suggest that the town was struck by a highly localised tsunami in the earthquake, apparently killing 20. This is interesting in part because it is quite likely such a localised event would have been caused by a (submarine?) landslide - not at all unusual in earthquakes. However, the before and after satellite images show the magnitude of the changes on the coastline in this area.

Before:


And after:


At first glance the change does not look so dramatic, but take a look at the location of the coastline in the before image in relation to the white building that I have highlighted below:


Actually, it is a little more interesting than you might initial suppose. First, note that the section of coast that has "disappeared" lies only between the two yellow dots that I have marked on the image above. To the east and the west the beach is intact. Second, take a look at this CNN video:



The key aspect is the picture of that lone tree standing upright in the ocean. A USGS report has suggested this is the site of a lateral spread (the same type of landslide that is evident in the port area of Port-au-Prince), which has caused the coastline to slip into the sea. As lateral spreads are essentially translational, a tree can remain upright. Unfortunately, as the coastline is now no longer protected by a beach, further erosion is likely. An interesting hypothesis is of course that this not-insubstantial slip caused the localised tsunami - or could it be that there was no wave at all, just the appearance of one to those people standing on the land as it slipped below the waves?

More El Salvador lahar satellite imagery

In an earlier post today I highlighted the availability of satellite imagery covering the El Salvador lahar disaster, triggered by Hurricane Ida earlier this month. Whilst sitting in a conference session this morning it occurred to me that the Disaster Charter, which provides satellite images for disaster relief and recovery operation, was also triggered by this event. So I had a quick look at the web page for this triggering of the charter, and sure enough there are some good materials there.

Perhaps the best image is this interpretation of the lahar tracks, produce using the Taiwanese Formosat2 satellite (famous for its images of Beichuan and Tangjiashan after the Wenchuan Earthquake) - do click on the image to see this properly, it is worth it!:

There is also a more detailed look at the town of Guadeloupe using the same satellite, showing before and after images of the town:

Viewed in conjunction with the NASA images in my earlier post, this is a very useful resource.

Satellite imagery of the El Salvador lahars

NASA has released before and after satellite images of the lahars (volcanic debris flows) triggered by Hurricane Ida in El Salvador earlier this month. The final toll of the landslides remains unclear, over 60 is the widely reported statistic.

The images are false colour composites collected by the ASTER instrument. These images differentiate between vegetation, which appears as red colours, and bare ground, which appear as a blue-grey colour. Such images are ideal for delineating new landslides, which usually strip away vegetation to leave bare soil.

This is the before image of the area affected by the landslides:

As usual, click on the image for a better view in a new window. Here is the image after the hurricanes passed through:


The lahar tracks are pretty clear. Note that they start high on the volcano, mostly with small, translational landslides. These slides then enter the channel, entraining (eroding and incorporating) material along the channel. The towns are quite clear on the images - the debris flows have hit the settlements in several locations, leaving this type of damage (Image from here):


When the landslides reach the plains below the volcano they spread out and stop, leaving a large area covered in debris. This is also clear on the image.

Chongqing landslide - NASA satellite image

NASA have provided the first decent overview of the Chongqing landslide via a high resolution satellite image. This can be found here.


The morphology of this is decidedly odd - I will spend some time trying understand it better. According to the NASA page the source is to the north and the landslide has moved southwards and then spread out to the southwest.

Meanwhile, the search for victims continues according to Xinhua.

The Pareechu landslide and flood, 2005

In July 2003 a landslide occurred on the Pareechu stream at 32.322N, 78.735E, a remote tributary of the Satluj River in Tibet (see Fig. 1). The landslide was quite large, blocking the river and allowing a lake to form that eventually breached. In this post I will try to use the range of satellite imagery and reports that are now available to describe the sequence of events.

Fig. 1: Google Earth location map of the Pareechu landslide (click on the image for a better view in a new window)

NASA produced an ASTER image of the site that was collected in October 2003, before the landslide occurred (Fig. 2). This shows the rather strange landform at this site - i.e. a broadening of the river in which there has clearly been extensive sedimentation.

Fig. 2: NASA ASTER image of the Pareechu landslide site before failure

It is not clear what triggered the landslide, but another ASTER image collected in July 2004 very clearly shows the immediate aftermath of the slide (Fig. 3).

Fig. 3: NASA ASTER image of the Pareechu landslide site after failure

Note that the basin is now being filled by a lake. The landslide itself is not particularly clear, although the extensive dust kicked up by the slide is fairly obvious as a whitish colour mantling the slopes just to the east of the lake. It is certainly clear that the valley is blocked. An enlargement of this area helps a little (Fig. 4).

Fig. 4: Enlargement of the NASA ASTER image of the Pareechu landslide site after failure

There is an image available in the following presentation (slide 7) that provides a view of the site in August 2004 (Fig 5):
http://www.managingclimaterisk.org/document/SAARC.pdf

Fig. 5: Presentation image of the Pareechu landslide site after failure

The landslide is clearer here, but note also that there is water flow clearly evident, so presumably at this point the landslide had overtopped the barrier. Note also though that the lake is still present, so presumably the flow was not large enough to induce significant erosion.

The next available image is from 20th February 2005 (Fig. 6). Of course this is the middle of winter, so unsurprisingly everything is frozen up. Nonetheless the lake is clearly still present.

Fig. 6: Google Earth image of the Pareechu landslide site in February 2005. The site is of course mantled with snow.

It does appear that there is some flow in the river, but not over the dam, presumably indicating that some seepage was occurring. This high resolution image also gives the first opportunity to get a good look at the slide, especially when the Google Earth terrain model perspective view is used (Fig. 7).

Fig. 7: Perspective Google Earth image of the Pareechu landslide site in February 2005.

It is clear that the landslide here was actually a comparatively small failure of a much larger rock slope failure. However, in turn this active section is part of a much larger rock slope failure that is delineated by a large fracture running across the hillside. I have highlighted this on Fig. 8.

Fig. 8: Annotated Google Earth image of the Pareechu landslide site in February 2005.

At its maximum the lake was 2,100 m long, 1,100 m wide and about 40 m deep storing about 64 million cubic metres of water, according to Gupta and Sah (2008). The dam appears to have failed at about 11 am on 26th June 2005, releasing a flood wave down the river that had a maximum measured discharge of about 2000 cubic metres per second. Fortunately, according to Gupta and Soh (2008) no lives were lost, although press reports at the time indicated that a small number of bodies were washed into India from Tibet. In India the flood did wash away 8 bridges, 15 km of road and caused damage estimated at US$177 million. It is not clear how much damage was caused in Tibet.

The final image, also from Google Earth and dated 4th September 2006, shows the site after the dam breach (Fig. 9).

Fig. 9: The most recent (Sept 2006) Google Earth image of the Pareechu landslide site

Note that the dam is still holding back a little water, but that this volume is now quite low. However, the slope above still looks highly unstable, so a repeat looks inevitable in due course.

Reference
Gupta, V. and Sah, M.P. 2008. Impact of the Trans-Himalayan Landslide Lake Outburst Flood (LLOF) in the Satluj catchment, Himachal Pradesh, India. Natural Hazards, 45, 379-90.