In a paper just published in the journal Landslides (Rengers et al.<\/em> 2020<\/a>), which is open access, the occurrence of landslides following wildfires in Southern California is investigated.\u00a0 The authors have looked at a 70 km\u00b2 area of the San Gabriel Mountains in Southern California, which was burned in the 2009 Morris fire, the 2014 Colby fire and the two wildfires that are collectively known as the 2016 San Gabriel Complex fire.\u00a0 None of the fires burned all of the study area, but some parts were burned by more than one of the fires.<\/p>\n The authors observed debris flows in the first year after a fire in the area that had been burnt.\u00a0 The example below, the Van Tassel watershed, highlighted by Rengers et al.<\/em> (2020)<\/a>, underwent extensive debris flow activity in early 2017 having been burnt the year before:-<\/p>\n Google Earth imagery showing the Van Tassel watershed after a wildfire in 2016, as highlighted by Rengers et al.<\/em> (2020)<\/a>. The area has undergone extensive debris flow activity, as evidenced by the deposits at the mouth of the canyon.<\/p><\/div>\n .<\/p>\n But the pattern of landslides in time is quite complex.\u00a0 Whilst debris flow activity was indeed high in the first year after a fire, triggered by heavy seasonal rainfall, debris flow activity rapidly declined with time. Three years after a fire, the primary type of landsliding had transitioned to shallow slips, with failures being triggered on both unburnt and burnt slopes.\u00a0 The density of landslides was highest in areas that had been burnt three years previously, whilst areas that had been burnt five years beforehand had a low density of landslides, similar to areas had not been burnt.<\/p>\n Where a second fire affected a previously burnt area, the density of landslides did not increase.\u00a0 A really interesting aspect of the landslides is they mostly occurred on slopes facing towards the south.\u00a0 Rengers et al.<\/em> (2020)<\/a> suggest that this may be because slopes facing away from the sun (i.e. to the north) in this semi-arid area regenerated vegetation quickly, reducing the likelihood of landslides.\u00a0 This is an important finding.<\/p>\n The study by Rengers et al.<\/em> (2020)<\/a> shows that wildfires do indeed lead to increased susceptibility to landslides triggered by rainfall.\u00a0 However, the response is more complex than might have been anticipated both in terms of the types of slides triggered and their spatial patterns.\u00a0 In this case the affect is quite shortlived. It is important to stress that this effect will be strongly controlled by local factors such as the topography, the geology and the climate, so responses in other locations might differ.\u00a0 I hope that this study will inspire similar investigations in other environments.<\/p>\n .<\/p>\n The number of bodies recovered from the Rajmala landslide in India<\/a> has increased to 49.\u00a0 The Indian Express has a good article about the background to the landslide<\/a>.\u00a0 It is now clear that this occurred late on 6 August rather than on 7 August, as had been reported previously.<\/p>\n .<\/p>\n The diversion route for the A83 at Rest and Be Thankful<\/a> was closed overnight due to concerns about another landslide<\/a>.\u00a0 The main road remains closed.<\/p>\n .<\/p>\n![\"Landslides](\"https:\/\/blogs.agu.org\/landslideblog\/files\/2020\/08\/20_08-wildfire-1.jpg\")
Quickslide 1: an update on the Rajmala landslide<\/h4>\n
Quickslide 2: Further problems at Rest and be Thankful<\/h4>\n
Reference<\/h4>\n