20 April 2022
UNOSAT analysis of the Leyte landslides from Tropical Storm Megi
The United Nations Institute for Training and Research (UNITAR) has published an initial satellite image analysis undertaken by the United Nations Satellite Centre (UNOSAT) of the landslides and flooding caused by Tropical Storm Megi in Leyte in the Philippines. This is based on 50 cm resolution Pleiades imagery acquired on 14, 16 and 17 April. The analysis is available to download.
Included in the analysis is imagery of some of the large landslides. One image shows the landslide at Bunga village, using an images dated 14 April 2022:-
The track length of this landslide is about 600 m, so it is a large failure. This has probably initiated as a shallow failure high on the hillside that entrained a large volume of material from the slope. It is interesting that the landslide appears to have initiated on a forested hillslope. The UNOSAT analysis suggests that 20 structures were destroyed or seriously damaged.
A second example is the Kantagnos village landslide, which I featured yesterday. The UNOSAT Pleiades image has captured the source area of the landslide:-
With a track length of about 3 km, this is a very large failure. The width of the source area is a surprise to me – this is a landslide that needs a much more detailed investigation. I wonder to what degree it would have been possible to anticipate a failure of this scale at this location. The before and after comparison in the imagery is quite sobering:-
Mapping of existing and potential landslides requires 3D imagery, but dangerous sites are often evident even in 2D images. But in the case of the Kantagnos landslide I would have struggled to identify this as a dangerous site on first inspection of the morphology of the slopes. The elements that might have made me suspicious are the areas that had been deforested for agriculture (and old landslide surface?) and, more importantly, those large, 90 degree bends in the river (has it been displaced by a landslide deposit?).
At Kantagnos, UNOSAT reports that 83 structures were destroyed or heavily damaged. The location has been declared to be uninhabitable. Inquirer.net reports that the latest information is that 59 people were killed at this site, and at least 63 remain missing.
The total toll from Tropical Storm Megi is now estimated to be 175 people, with a further 110 missing. Recovery operations have been terminated at most locations.