Google Earth Blog

The amazing things about Google Earth


landslide

Landslide and Tsunami in Greenland

Last Saturday, on 17th June, a landslide in Greenland caused a tidal wave, killing four people and injuring nine in the community of Nuugaatsiaq. Two other communities, Igdlorssuit and Viaqornat, were apparently affected. Read more about it on the Landslide Blog.

We thought it would be interesting to see the area in Google Earth using Sentinel-2 imagery. We downloaded the Sentinel-2 image from 19th June, 2017 and imported it into Google Earth:


The relative positions of the landslide and Nuugaatsiaq.Copernicus Sentinel data, 2017.

The distance between the landslide and the village of Nuugaatsiaq is about 30 km. Igdlorssuit is about 60km from the landslide site and Viaqornat just over 100 km.


The region as seen in Google Earth imagery.


The village of Nuugaatsiaq as seen in a DigitalGlobe image from 2012.

Here is a YouTube video showing the Tsunami arriving at Nuugaatsiaq:

To see the relevant section of the Sentinel-2 image in Google Earth, download this KML file
.

A Landslide in California with Planet Imagery

We love Landsat and Sentinel-2 imagery for their easy accessibility and global coverage, but they are rather low resolution at 10 m per pixel for Sentinel-2 and 15 m per pixel for Landsat. Commercial satellite imaging company Planet, now covers the globe with greater regularity and higher resolution (typically about 3 m per pixel) and for the US state of California, releases the imagery under creative commons licence within a couple of weeks of capture. We recently came across a large landslide that occurred along the Californian coast in an area known as Big Sur.

We were able to find it in Planet’s tool ‘Planet Explorer’ for browsing their imagery. You need to sign up to view daily imagery, but signup is easy and free.


The Big Sur Landslide as seen in Planet imagery.

Once you have signed up you can try going here to see the location in Planet Explorer. Try comparing before and after images with the built in ‘compare’ feature.

The Kurbu-Tash and Ayu landslides in Kyrgyzstan

In March this year we had a look at landslides in Kyrgyzstan and noted just how frequent landslides there appear to be.

Just a month after that post, two more major landslides occurred to the southeast of the region we looked at before. On April 24th a very large landslide engulfed the village of Kurbu-Tash, burying 11 houses, a school, a kindergarten, a mosque and a medical facility. Luckily, nobody appears to have been harmed in that event. Then on April 29th, a much smaller but more deadly landslide, killed 24 people in the village of Ayu. For more on both landslides, including ground level photos and video, see The Landslide Blog (1 2 3).

You can see before and after images using Landsat imagery on NASA’s Earth Observatory website. However, the latest Landsat image was not available on Amazon Web Services at the time of writing, so we instead got a Sentinel-2 image of the location. Here is a ‘before and after’ of the Kurbu-Tash event.

before
after

Left: CNES / Airbus image from Google Earth. Right: Sentinel-2 image dated May 19th, 2017.

The landslide flowed south to north, burying buildings near the end of its run. The total length of the landslide is around 5 km. Also note the small lake that has formed uphill from the landslide. This is known as a ‘landslide dam’, a topic we covered last year. Such dams can be potentially catastrophic if enough water builds up, overflows and suddenly erodes the dam.

The Ayu landslide is much harder to spot. In fact, we can see at least five other landslides nearby, some of which were larger.

This report states that prior to the Ayu landslide, the Osh region has had at least 25 landslides so far this year, killing six people.

For the locations above, including image overlays using portions of the Sentinel-2 image and the locations of the many landslides we found, download this KML file

The Mocoa Landslide in DigitalGlobe imagery

According to Wikipedia, during the pre-dawn hours of 1 April 2017, locally heavy rain triggered flash flooding and landslides in the city of Mocoa, Putumayo, Colombia, killing at least 316 people, injuring 332, and leaving 103 others missing. Technically, the tragedy was not a landslide but rather a mud-flow triggered by many landslides. For some analysis of the cause of the tragedy see the Landslide Blog. It was predicted in 2014.

DigitalGlobe, as part of its Open Data program, has recently released satellite imagery of the location. Although we knew about the event soon after it happened, we had not expected to see any imagery as Mocoa is in a region that has near constant cloud cover, making it difficult to photograph.

DigitalGlobe provides the imagery divided up into squares of 1Gb files with no compression. So even a completely black square that is off the edge of the main image is a 1Gb download! There is a preview of the whole image, but we still ended up downloading almost all the squares to find the right ones as there are no previews of the individual squares.


Mocoa, Colombia, as seen in DigitalGlobe imagery.


Keep in mind that what we are seeing is the debris left behind from the flood. The actual flood waters probably covered some of the houses.

We didn’t download the ‘before’ images from DigitalGlobe so we haven’t done a ‘before and after’. The imagery in Google Earth is so old that such a comparison is not very informative as the town had expanded considerably since the last Google Earth image.

We have cropped and compressed the part of the imagery showing the town of Mocoa and created an image overlay for you to view in Google Earth.

Kyrgyzstan landslides in Google Earth

On April 27th, 2016, a landslide occurred in Kyrgyzstan and was captured on video as you can see below. The Landslide Blog also wrote about it here and here. We have been keeping an eye on the location and Google has recently updated the imagery.

before
after

Before and after of the landslide in the video.

Having looked around the area it is clear that the region is very susceptible to landslides, with evidence of past landslides almost anywhere you look. Unfortunately, there is not a lot of imagery and most of the landslides took place before the earliest image. We did find one more that took place in 2016, although it is not quite covered by the latest image.

before
after

Before and after of another landslide that occurred in 2016.

Apart from the immediate danger from landslides, there is also the phenomenon of landslide dams, examples of which we have looked at before. A landslide dam occurs when the landslide blocks a river, creating a lake behind it and a catastrophic flood may occur when the dam gives way. We had a look around the region and found several cases where there probably was a small landslide dam and there is significant risk of such disasters in the future.


This landslide blocked the river, which has since carved a channel through the debris.

In the picture above, the slope has been slipping for many years and may never have caused a landslide dam, but the risk is clearly significant as a dam would result in the flooding of the nearby houses and its collapse could cause flooding downstream. Just a little further upstream it looks as if part of the town is slowly sliding into the river:


Also note the smaller landslide on the opposite bank which could potentially have created a landslide dam.

To find the above locations in Google Earth, download this KML file. We have marked some of the more notable landslides that we found, but there are many more in the region.

According to this video, a significant cause of the landslides is deforestation, followed by uncontrolled grazing. Trees and other plant cover helps to stabilize slopes.