{{Infobox eruption | name = 1996 eruption of Gjálp | image = Skeidara.jpg | caption = Gjálp eruption: Jökulhlaup 1996 over Skeiðarársandur, the piedmont glacier Skeiðarárjökull and Öræfajökull in the background | start_date = 30 September 1996 | end_date = 13 October 1996 | volcano = Gjálp | type = Subglacial fissure eruption | location = Western Vatnajökull | coordinates = <ref>A. Jarosch et al.: Progressive cooling of the hyaloclastite ridge at Gjálp, Iceland, 1996–2005. Journal of Volcanology and Geothermal Research** 170 (2008) 218–229</ref> | VEI = 3 | map_caption = Location of main volcano Grímsvötn within Vatnajökull | impact = Jökulhlaup over Skeiðarársandur, Hringvegur partially destroyed }} Gjálp () is a hyaloclastite ridge (tindar) in Iceland under the Vatnajökull glacier shield. It originated in an eruption series in 1996 and is probably part of the Grímsvötn volcanic system,See also GVP: Grimsvotn. Eruptive history. Retrieved 29 August 2020. though not all the scientists involved are of this opinion. Importance The eruption was of imminent importance, because it was for the first time that a subglacial eruption under a thick ice cover as well as the connected jökulhlaup could be observed and analyzed by modern techniques.See also: Hugh Tuffen, D.W. McGarvie, etal.: Will subglacial rhyolite eruptions be explosive or intrusive? Some insights from analytical models. Annals of Glaciology, in press. Lancaster University. (2006) Retrieved 30 August 2020. Geography Eruption location The subglacial eruption fissure is to be found in the northwest corner of Vatnajökull ice cap more or less half way between the central volcanoes Bárðarbunga and Grímsvötn. Vatnajökull ice cap The Vatnajökull glacier which covered the location at time of eruption had a thickness of 500–600 m. In other places the glacier shield can have thicknesses of up to 900 m. Vatnajökull covered an area of 8.200 km2 in 1996, but it is retreating and measured just 8.100 km2 in 2007. The glacier is temperate, lies in lower elevations and is therefore sensible to climatic changes. As a consequence it has been advancing and retreating since the Weichselian glaciation. Its last advance took place during the so called Little Ice Age from the 13th to the end of the 19th century and since then it is retreating. Parts of two volcanic zones of Iceland are placed under Vatnajökull, ie. the very active East Volcanic Zone (connected to rifting at the divergent plate boundary in Iceland), responsible for the highest number