8 February 2022
Planet Labs imagery of the 31 January 2022 mudflow in the La Gasca suburb of Quito
Posted by Dave Petley
Planet Labs imagery of the 31 January 2022 mudflow in the La Gasca suburb of Quito
Last week I posted about the 31 January 2022 mudflow at La Gasca in Quito, Ecuador. Two loyal readers, Stephen Slaughter and Doug Clark, have kindly highlighted that a few days ago the sky was sufficiently clear for Planet Labs to capture a good PlanetScope image of the site, which is revealing:-
PlanetScope image of the site of the 31 January 2022 mudflow at La Gasca in Ecuador. Image collected on 3 February 2022, copyright Planet Labs, used with permission.
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The track of the mudflow, in an existing channel, is clear, running approximately west – east across the middle of the image. It is clear that the volume was increasing along the track and just to the east of the centre of the image it appears to bifurcate. On the eastern side of the image the damage to the city can be seen, although with little detail. Interpretation is helped considerably by a drone video on the El Comercio website, which shows that the mudflow followed the incised channel to the north of the vegetated area just south of Teresa Silva, and then directly down the road network.
The resolution of PlanetScope images makes interpretation of mechanisms of initiation quite difficult, but it is interesting to take a look at the upper parts of the channel:-
PlanetScope image of the upper part of the channel of the 31 January 2022 mudflow at La Gasca in Ecuador. Image collected on 3 February 2022, copyright Planet Labs, used with permission.
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There is no obvious landslide on the terrain adjacent to the channel that might have been the initiating event for the mudflow. It seems likely therefore that it started either as a very localised failure that is too small to resolve or as an in-channel event in which the flow initiated bank erosion and/or entrainment of the channel bed. It is clear that the majority of the mudflow that struck La Gasca was formed from material eroded from within the channel.
With climate change causing an increase in rainfall intensity, there is a high likelihood of a repeat of this event. Mitigation of the channel is needed, along the line of the Japanese sabo engineering approach (ideally using more environmentally-conscious engineering approaches than is sometimes the case).
Finally, many thanks to Stephen and Doug for highlighting the imagery to me. Finding time to write this blog is a challenge at times, it is made so much easier when loyal readers provide help like this.
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Reference
Planet Team (2022). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://www.planet.com/
Dave Petley is the Vice-Chancellor of the University of Hull in the United Kingdom. His blog provides commentary and analysis of landslide events occurring worldwide, including the landslides themselves, latest research, and conferences and meetings.
I was in this area in 2013. See this map link: https://www.google.com/maps/@-0.1837377,-78.5192071,2100m/data=!3m1!1e3 .
At the bottom of the picture, just above “Volqano Park” is the location of the flash flood/debris flow.
We visited “Rumiloma” (labeled on the map) in the ravine/canyon at the top of the map view. Driving up that canyon, which has a much larger watershed, we saw a check dam (visible about 1000 feet downstream of Rumiloma on the map). The area just upstream of the dam was a grassy football/soccer field and completely dry – obviously this structure is for floods like what just occurred in La Gasca. The topography of this area is very steep.
Here is a link with Rumiloma and the check dam below:
https://www.google.com/maps/@-0.1778189,-78.5222414,414m/data=!3m1!1e3
They’ve done a lot of work in this area but the proximity of urban areas, the topography, and the humid high altitude climate must be a big challenge in mitigating risk.
Depending on how local that downpour was, it would be interesting to see the Planetscope view of that check dam and whether it captured sediment and debris. It’s ~just~ off of the top of the first Planetscope image in this post.
@Steve: the resolution on the Feb. 3 Planet.com web page isn’t quite sufficient to say with any confidence whether the check dam that you mention was affected by a debris flow (e.g., you can’t really see the soccer field as such). Comparing it to the most recent pre-debris flow image that is cloud free for that site (Jan 18), however, the proximal side of the dam (where the soccer field is) doesn’t appear to have changed much if at all, suggesting it wasn’t affected by a similar debris flow..