Impacts and dynamics of volcanically-generated jokulhlaups, Eyjafjallajokull, Iceland

Eyjafjallajokull是冰岛南部一座高1666米、被冰川覆盖的层状火山，已知在历史记录中曾四次喷发：公元500年、公元920年、公元1612年和公元1821-23年。每次火山喷发都导致冰川迅速而大规模的融化，产生非常大的冰川爆发洪水（冰川爆发洪水），峰值流量为10^3-10^4 m^3s^ 1，淹没了周围人口稠密的低地。2010年3月3日，冰岛气象局（IMO）通知我们，在Eyjafjallajokull火山下有一段时间的地震活动增强（从2010年1月初开始）。基于地震活动和地面变形率呈指数增长的假设，我们收集了2010年3月9日至16日期间许多可能的jökulhlaup路径的喷发前地面激光扫描仪和dGPS调查数据。数据采集期结束五天后（2010年3月20日），岩浆沿着一条新形成的500米长的裂缝到达地表，该裂缝位于Fimmvorduháls山口以北，正位于Eyjafjallajokull冰盖以东。这一阶段的喷发发生在非冰覆盖区域，活动于4月12日停止。仅仅两天后（格林尼治标准时间4月14日02:00），埃亚菲亚德拉火山2.5公里宽的山顶火山口（在原始裂缝喷发的西面）下开始了一次大规模的冰下爆炸性喷发。几小时内，火山喷发融化了200米的冰盖，形成了一个8.5公里高的火山柱（随后对泛欧空中交通产生了严重影响）。到格林尼治时间4月14日07:00，埃亚菲亚德拉冰盖的迅速融化产生了火山喷发的冰川，分别从Gigjokull和nupakottsdalur倾泻而下，位于埃亚菲亚德拉冰盖的南北两侧。几小时后，最初的冰川在马克弗约特河系统中达到峰值，破坏了冰岛在马克弗约特桥附近的主要环城公路。随后，火山喷发强度的增加产生了反复的冰川喷发，淹没了马卡洛夫火山。在4月15日格林尼治标准时间18:55的一次飞行中，马修·罗伯茨博士（冰岛气象局和项目合作伙伴）目睹了Gigjokull巨大的jokulhlaup（峰值流量约为10^4 m^3s^-1），这促使整个Markarfljot地区的人口立即撤离。这个冰川“充满了沉积物”，其特征是一个粘性的、表面光滑的、叶状的流锋，随后是一个更湍流的流体流体。这些初步观察表明，这次冰川的锋面波高度集中。在这个项目中，我们的目标是提高对冰下火山喷发所造成的火山成因的jokulhlaup影响和过程的理解。为了做到这一点，我们将获取Gigjokull前冰川区和Markarfljót的jokulhlaup后数据，与我们直接喷发前（2010年3月9日至16日）的完整3D TLS地形数据集进行比较。因此，我们有一个前所未有和独特的机会：(1)准确量化一系列jokulhlaups的地貌和沉积特征；(2)利用这些特征来了解和验证我们对一系列火山jokulhlaups的水动力学特征的重建，这些火山jokulhlaups能够产生山谷规模的地貌和沉积影响。要做到这一点，我们需要重新调查那些我们有重要基线数据，但火山成因jokulhlaup影响和过程的证据是短暂的地区（因此向NERC提出了紧急申请）。该项目的第二个重要阶段将使用这些数据来模拟火山喷发对流出系统的影响。

Eyjafjallajokull, a 1666 m high, glacier-clad, stratovolcano in southern Iceland, is known to have erupted on four previous occasions in the historic record: ~500 AD, ~920 AD, 1612 AD and 1821-23 AD. Each eruption has resulted in rapid and large-scale glacier ice melt, generating very large jokulhlaups (glacier outburst floods) with peak discharges of 10^3-10^4 m^3s^-1 inundating the surrounding populated lowlands. On March 3rd 2010, the Icelandic Meteorological Office (IMO) informed us of a period of enhanced seismic activity under Eyjafjallajokull (since the beginning of January 2010). Based on the assumption that the exponential increase in both seismic activity and rates of ground deformation represented pre-eruption behaviour and intrusion of a magma tongue into the Earth's crust at this location, we collected pre-eruption Terrestrial Laser Scanner and dGPS survey data from a number of probable jökulhlaup routeways between March 9th and 16th 2010. Five days after the end of this data acquisition period (on March 20th 2010), the magma reached the surface along a newly formed 500 m-long fissure located north of Fimmvorduháls pass and directly east of the Eyjafjallajokull ice cap. This phase of eruption was on a non-ice covered area and activity ceased on April 12th. Only two days later (April 14th at 02:00 GMT) a large subglacial explosive eruption started beneath the 2.5 km-wide summit caldera of Eyjafjallajokull (to the west of the original fissure eruption). Within hours the eruption melted through 200 m of the ice cap and became fully phreatic, producing a major 8.5 km-high volcanic plume (with subsequent serious implications for pan-European air traffic). By 07:00 GMT on April 14th, rapid melting of the Eyjafjallajokull ice cap generated volcanogenic jokulhlaups that cascaded from Gigjokull and down Nupakotsdalur on the northern and southern flanks of Eyjafjallajokull respectively. The initial jokulhlaup from Gigjokull reached peak discharge in the Markarfljot river system several hours later, damaging Iceland's main ring road near the Markarfljot bridge. Subsequent increases in eruption intensity generated repeated jokulhlaups from Gigjokull that inundated the Markarfljot. On an overflight at 18:55 GMT on April 15th, Dr Matthew Roberts (Icelandic Met Office & project partner) witnessed an enormous jokulhlaup (peak discharge ~ 10^4 m^3s^-1) from Gigjokull which prompted the immediate evacuation of the population within the entire Markarfljot area. This jokulhlaup was 'sediment-laden', characterised by a viscous, smooth-surfaced, lobate flow front followed by a more turbulent fluid flow body. These initial observations suggest that the frontal wave of this jokulhlaup was hyperconcentrated. In this project, we aim to improve understanding of volcanogenic jokulhlaup impacts and processes due to a subglacial volcanic eruption. In order to do this, we will acquire post-jokulhlaup data for the Gigjokull proglacial area and the Markarfljót to compare against our directly pre-eruption (9th -16th March 2010), full 3D TLS topographic datasets. We therefore have an UNPRECEDENTED and UNIQUE OPPORTUNITY to (1) accurately quantify the geomorphological and sedimentary characteristics of a series of jokulhlaups and (2) to use these to inform and validate our reconstructions of the hydrodynamic characteristics of a series of volcanogenic jokulhlaups capable of valley-scale geomorphological and sedimentary impact. To do this, we need to re-survey areas for which we have important baseline data but where the evidence of volcanogenic jokulhlaup impacts and processes is transient (hence this Urgency application to NERC). A second and important phase of the project will use this data to model the impacts of the eruption on the outflow system.