Jökulhlaup

Jökulhlaup (floods from glaciers) often follow eruptions underneath glaciers. Such is the case for Öræfajökull volcano, which stands over 2000m high, covered by an ice cap above. During an eruption the hot magma melts a significant amount of glacial ice and generates a sudden jökulhlaup. These types of floods can be immensely powerful and very destructive. Floods related to the 1362 and 1727 eruptions from Öræfajökull volcano, rushed down the surrounding steep hills as a mixture of water, debris, ash and chunks of glacial ice. The aftermath of the second flood can be seen all around us, covering an area over 25km². 

The 1727 glacial outburst flood and formation of kettle holes in Háalda . 

The jökulhlaup that followed an eruption in Öræfajökull in 1727 rushed down the canyon in front of us and into the Kotá river channel. Just before exiting the river channel and spreading out over open land the flood reached an impressive size of about 220-280m wide and 20m deep. As it reached the lowland plains it flowed south as a sheet of water over land and into the sea. As the jökulhlaup shallowed, icebergs and material started to anchor into the sandy flood plain. By the end the flood plain was covered with icebergs and larger chunks of ice. 
The pit in front of us is one of two kettle holes that were formed as two large icebergs anchored into the sand bank we are standing on. It took months for icebergs lying at the floodplain surface to melt but for buried ice it could take a few decades to melt. Subsequently they leave these permanent marks behind known as kettle holes or iceberg pits, Háalda has been a protected natural monument since 1975 and is a reminder of the immense jökulhlaup. 

The 1362 glacial outburst flood and Litla - Hérað 

The jökulhlaup following an eruption in Öræfajökull volcano in 1362 rushed down Falljökull, Virkisjökull, Kotárjökull and Kviárjökull in the south eastern part of Öræfajökull. At that time a blossoming sparse farm and village community known as Litla - Hérao thrived at the roots of Öræfajökull. Along with immense ash fall and pyroclastic flows the jökulhlaup had a part in destroying the farming grounds and desolating Litla-Hérad. Many centuries later people settled and started farming in the area again, the land is now part of the Hornafjörður municipality and is called Öræfi.

Geological

Kettles are fluvioglacial landforms occurring as the result of blocks of ice calving from the front of a receding glacier and becoming partially to wholly buried by glacial outwash. Glacial outwash is generated when streams of meltwater flow away from the glacier and deposit sediment to form broad outwash plains called sandurs. When the ice blocks melt, kettle holes are left in the sandur. 

Emergence of Jökulhlap - Kettle Hole

	Glacier [1] advances forward, sediment [2] is thrust up from underneath the glacier margin.
	Jökulhlaup [4] bursts out from underneath and through the glacier. The jökulhlaup transfers icebergs [3], sediment and ash.
	The jökulhlaup subsides and the glacier [1] becomes stable again. Icebergs [3] anchor and get buried in the flood plain.
	Icebergs [3] buried into the flood plain. The sediment insolates the icebergs and it can take multiple years for the ice to melt. The glacier [1] shrinks and starts to retreat.
	Years or tens of years later the ice has melted and iceberg pits [5] have formed on the surface of the flood plain. The glacier retreats further in land and leaves behind an end moraine [6] which marks the former position of the glacier margin.

In order to log this cache, please email the cache owner the answers to the following questions: 

1. How many kettle holes do you see?
2. What is the circumference of the largest hole?
3. Describe in your own words the creation of the kettle holes!
4. In which year was Háalda natural monument?
5. Take a photo of you or your GPS near the kettle holes.