{"id":442,"date":"2011-11-03T15:59:01","date_gmt":"2011-11-03T15:59:01","guid":{"rendered":"http:\/\/all-geo.org\/volcan01010\/?p=442"},"modified":"2011-12-02T20:43:27","modified_gmt":"2011-12-02T20:43:27","slug":"why-people-are-scared-of-katla","status":"publish","type":"post","link":"https:\/\/all-geo.org\/volcan01010\/2011\/11\/why-people-are-scared-of-katla\/","title":{"rendered":"Why people are scared of Katla"},"content":{"rendered":"

Note: 02 December 2011.<\/strong>
\nThe current media interest in Katla does not stem from a recent change in activity at the volcano, but from an article published on the BBC website<\/a> today.\u00a0 The same thing followed a Guardian article<\/a> earlier in the year.\u00a0 Activity at Katla is still elevated, as it has been for six months already<\/a>.\u00a0 There is no new evidence today that an eruption is likely very soon.\u00a0 In geological terms, imminent could mean weeks, months, or maybe years.\u00a0 This post was written in early November.<\/p><\/blockquote>\n

Katla rumbles on.<\/p>\n

The unrest began in the summer, when a small flood broke out from beneath the glaciers and washed away the bridge<\/a> over the M\u00falakv\u00edsl river.\u00a0 Since then, there have been a number of small earthquakes every day.\u00a0 This is more activity than usual, but less than, for example, occurred at Eyjafjallaj\u00f6kull in the weeks before the 2010 eruption.\u00a0 It is not clear where this is heading, but Iceland continues to prepare for an eruption and local towns have been running evacuation drills<\/a>.<\/p>\n

\"The

The remains of the bridge at M\u00falakv\u00edsl that was washed away in the flood of July 2011, with the replacement bridge in the background. Note the yellow earth-moving equipment high on the hillside. They aren't parked up there for the view.<\/p><\/div>\n

While the international media focus on the potential ash cloud and ‘travel misery’, the real destruction in Iceland will be caused by meltwater floods.\u00a0 Katla is covered by glaciers up to 500 m thick.\u00a0 These represent a huge reservoir of water, waiting to be unlocked by the heat of an eruption.\u00a0 A look at floods from the last time round, in 1918, gives an indication of what could be expected.<\/p>\n

The j\u00f6kulhlaup from the 1918 eruption<\/h3>\n

There is a word in Icelandic for such floods from beneath the ice: j\u00f6kulhlaup<\/em>.\u00a0 Translated directly into English, it means glacier leap<\/em>.\u00a0 This seems appropriate, as the water bursting under, over and through the ice tears off huge chunks and carries them suddenly forward down the valley. When the water subsided after the flood of 1918, the plain was strewn with giant icebergs, up to 60-80 m high.<\/p>\n

Eyewitnesses said the speed of the Katla 1918 j\u00f6kulhlaup was “so great that a fit man could not have avoided it”.\u00a0 Escaping from the eastern side of the glacier, the flood wave reached the ocean in 45 minutes.\u00a0 These reports correspond to a speed of 10 metres per second (36 km per hour).\u00a0 The high-water mark of the j\u00f6kulhlaup is recorded on the slopes of small hills along the way that were scoured clean by the swirling torrent.\u00a0 Near the glacier, the waters peaked at 25 metres deep.<\/p>\n

Haukur T\u00f3masson<\/a> combined velocity and the depth of the flood with the shape of the channel and came up with an estimate for the peak discharge of 300,000 cubic metres per second.\u00a0 The total volume of water was estimated to be around 8 cubic kilometres.\u00a0 The flooded area was as much as 700 square kilometres.\u00a0 There was sufficient sediment in the flow to extend the coastline by 5 kilometres.<\/p>\n

To put these figures in context, the average discharge of the Mississippi is a relative trickle at 17,000 cubic metres per second!\u00a0 The flood is equivalent to pouring out Loch Ness<\/a> onto an area half the size of Greater London in less than 8 hours.<\/p>\n

The j\u00f6kulhlaup from the next eruption<\/h3>\n

To understand the hazard from future flooding<\/a>, researchers in Iceland used computer models to simulate what would happen if another Katla 1918-sized flood was to occur at the volcano.\u00a0 They found that floods would reach the roads to the east of the volcano in 1-1.5 hours after the eruption began; a very short window to get people to safety.\u00a0 Few people live in this region, but destruction of the road would be a major blow for the tourism-based economy of the area.<\/p>\n

Iceland is a country about the size of Ireland.\u00a0 For 9 months of the year, you cannot cross the middle as the roads are blocked by snow.\u00a0 Highway 1 is the tarmac ring-road that runs around the country near the coast.\u00a0 If it is destroyed, it means that you can no longer drive directly from V\u00edk in the south, to H\u00f6fn<\/a> in the south east (271 km, about 3 hours).\u00a0 Instead, you have to go all the way round<\/a> the other way (1068 km, about 13 hours).\u00a0 A severe j\u00f6kulhlaup could close the road for months.<\/p>\n

The models showed that a flood travelling westward would sweep across the farmlands of the Landeyjar district, which is home to around 600 people, within 3-10 hours.\u00a0 Homes, farms and livestock would be destroyed.\u00a0 Fortunately, investigation of deposits from past j\u00f6kulhlaups in the region suggest that this area is flooded rarely, perhaps only once every 500-800 years.<\/p>\n

\"katla_jokulhlaup_times\"<\/a>

Predicted times for Katla flooding from 1918-sized j\u00f6kulhaup. Click to enlarge. Source: Gudmundsson, M. T., G. Larsen, \u00c1. H\u00f6skuldsson, and \u00c1. G. Gylfason (2008), Volcanic hazards in Iceland, J\u00f6kull, 58(58), 251-268.<\/p><\/div>\n

Summary in a single picture<\/h3>\n

\"WhySources:<\/em> Amazon map – Natural Earth data<\/a>; Iceland map – atlas.lmi.is<\/a>; Iceberg image – Larsen, G. (2010)<\/a>, 3 Katla: Tephrochronology and Eruption History.<\/p>\n","protected":false},"excerpt":{"rendered":"

Note: 02 December 2011. The current media interest in Katla does not stem from a recent change in activity at the volcano, but from an article published on the BBC website today.\u00a0 The same thing followed a Guardian article earlier … Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":3,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-442","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/all-geo.org\/volcan01010\/wp-json\/wp\/v2\/posts\/442","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/all-geo.org\/volcan01010\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/all-geo.org\/volcan01010\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/all-geo.org\/volcan01010\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/all-geo.org\/volcan01010\/wp-json\/wp\/v2\/comments?post=442"}],"version-history":[{"count":26,"href":"https:\/\/all-geo.org\/volcan01010\/wp-json\/wp\/v2\/posts\/442\/revisions"}],"predecessor-version":[{"id":510,"href":"https:\/\/all-geo.org\/volcan01010\/wp-json\/wp\/v2\/posts\/442\/revisions\/510"}],"wp:attachment":[{"href":"https:\/\/all-geo.org\/volcan01010\/wp-json\/wp\/v2\/media?parent=442"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/all-geo.org\/volcan01010\/wp-json\/wp\/v2\/categories?post=442"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/all-geo.org\/volcan01010\/wp-json\/wp\/v2\/tags?post=442"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}