{"id":7968,"date":"2014-02-11T08:47:09","date_gmt":"2014-02-11T08:47:09","guid":{"rendered":"http:\/\/blogs.agu.org\/landslideblog\/?p=7968"},"modified":"2014-02-11T08:47:09","modified_gmt":"2014-02-11T08:47:09","slug":"southern-england-landslides","status":"publish","type":"post","link":"https:\/\/blogs.agu.org\/landslideblog\/2014\/02\/11\/southern-england-landslides\/","title":{"rendered":"Southern England: the potential for movement in deep-seated landslides"},"content":{"rendered":"
Extreme rainfall in southern England<\/h5>\n

Southern England is currently undergoing an extraordinary period of exceptional rainfall, especially in the south, which is causing floods on an unprecedented scale<\/a>.\u00a0 This rainfall, which is likely to be a consequence of climate change<\/a>, shows no signs of abating, with further heavy falls expected over the next few days<\/a>.\u00a0 Not surprisingly there have been many landslides, especially on the coast and along railway lines, and more can be expected. The UK Met Office provides monthly precipitation data for Southern England <\/a>.\u00a0 I have downloaded the data and plotted the monthly time series from 1910 (the start of the dataset):<\/p>\n

\"Southern<\/a><\/p>\n

..<\/p>\n

The horizontal line in the long-term mean value (77.3 mm).\u00a0 The 2014 total, at 165.4 mm, is 2.8 standard deviations from the mean – a truly exceptional value. And of course it is still raining, such that since the end of January the floods have got much, much worse.<\/p>\n

Deep-seated landslides in southern England<\/h5>\n

From a landslide perspective an interesting aspect of this is the likely behaviour over the next two or three months of the deep-seated landslide systems that lie along the southern coast of the UK.\u00a0 So far there have been few reports of these landslides showing substantial movements.\u00a0 However, typically deep-seated landslides show a long lag between the rainfall and the activation of movement.\u00a0 I can illustrate this with a dataset for a very deep-seated landslide on the Isle of Wight<\/a> on the very southern tip of the UK.\u00a0 The landslide, at Ventnor (shown below), is very well known and has been extensively studied<\/a>.\u00a0 It sits under most of the town:<\/p>\n

\"Southern<\/a><\/p>\n

..<\/p>\n

My former student, Jon Carey, studied this landslide for his PhD.\u00a0 In particular he monitored a phase of movement of the landslide complex from a decade ago.\u00a0 His thesis, which is excellent, is available for download from the Durham ethesis site<\/a>. \u00a0 The landslide moves slowly – very slowly indeed in fact – so the level of risk for the population is low, although the town does suffer some periodic damage to buildings.\u00a0 The landslide is carefully monitored.\u00a0 This is a graph of movement rate of the landslide compared with monthly rainfall from 2000-2001:<\/p>\n

\"Southern<\/a>

From Carey, J. (2011): http:\/\/etheses.dur.ac.uk\/3186\/
Page 342<\/p><\/div>\n

..<\/p>\n

The monthly rainfall peaked in October and November 2000, and then fell to lower levels in the period November to January.\u00a0 However, the movement of the landslide only really started to accelerate in November 2001 and reached a maximum in early January.\u00a0 It then continued to move at a higher rate right through to the end of April, probably helped by a further wet month in February.\u00a0 So the lag between the rainfall and the movement was two to three months<\/p>\n

Now, as noted above, for this landslide the movement rates are very slow (typically 0.1 mm per day), so the impact is low.\u00a0 However, there are many other deep-seated landslides in the UK that can show much higher rates of movement – this is the spectacular (and fortunately uninhabited) Black Ven landslide in Dorset (see this post on the old home of this blog for a description of this landslide<\/a>):<\/p>\n

\"Southern<\/a>

Photograph of the Black Ven landslide in Dorset. From Brunsden et al 1988: Landshapes. David and Charles, Newton Abbot.<\/p><\/div>\n

..<\/p>\n

So, we might expect to see some interesting landslide movement on the next few weeks and even months as ground water levels continue to rise in these deep-seated landslide complexes.<\/p>\n","protected":false},"excerpt":{"rendered":"

The current exceptional rainfall in southern England will be driving up groundwater levels. Deep-seated landslides typically activate 2-3 months later<\/p>\n","protected":false},"author":22,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-7968","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/posts\/7968","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/users\/22"}],"replies":[{"embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/comments?post=7968"}],"version-history":[{"count":0,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/posts\/7968\/revisions"}],"wp:attachment":[{"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/media?parent=7968"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/categories?post=7968"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/tags?post=7968"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}