Askja is a caldera (sunken crater) in a central volcano in the Dyngjufjöll Mountains. It is the centre of a volcano system with many fissures, including the Sveingjár crater row.
The mountains emerged in eruptions under an Ice Age glacier cap. Askja itself was formed, for the most part, at the end of the Ice Age in a major ash eruption which caused the roof of the magma chamber at the heart of the central volcano to subside. A deep circular depression remained that gradually began to fill with lava from subsequent eruptions around the rim of the depression. The bottom of Askja is currently at an altitude of 1100 m while the rim is 1300-1500 m above sea level. The term askja(the Icelandic word for caldera) is used in the names of many similar formations in other locations.
Lake Askja is the deepest lake in Iceland with a depth of more than 200 m. It was formed in 1875 when a powerful eruption occurred in the south of the caldera. Almost 2.5 cubic kilometres of volcanic material surged up from the vent in just a few hours. The process was similar to the sequence of events that originally created Askja. After the eruption, the magma chamber ceiling began to subside, eventually stopping almost 250 metres below its initial level. The depression filled with ground water and Lake Askja was formed.
Between 1922 and 1929, several small eruptions occurred around the edge of the new depression.
Víti - warm lake in a crater
In fact, the caldera contains several volcanoes, including Víti, a maar (explosive volcanic crater) formed at the end of the eruption in 1875. Water has accumulated in the crater. Its temperature is variable, depending on how much meltwater is discharged into it in springtime - it is around 30°C on average. The depth of the water is greatest at the centre, more than 8 metres. Víti is a popular bathing site, but if you intend taking a dip, please be aware that the sloping path is very slippery in wet weather and the mud at the bottom is quite hot, especially on the eastern bank. There is also a danger of rocks falling from the edges.
Eruptions and lava
Askja has erupted several times in recorded history. It played a significant part in driving people away from East Iceland after 1875. The most recent eruption in Askja was in 1961 when lava flowed across Vikrahraun. American astronauts trained in this area - the landscape was thought to be similar to that on the moon.
The lower slopes of Askja are covered with rough aa lava.
In 1907, a group of German scientists embarked on a scientific expedition to Askja. The expedition was led by geologist Walter von Knebel, accompanied by Hans Spethmann, a student of geology, and the painter Max Rudloff. Two of the group, Knebel and Rudloff, disappeared on 10 July 1907. They are presumed to have drowned while conducting research using a poorly constructed canvas boat. Spethmann was engaged in geological research in the mountains north-east of the lake on the day of the accident.
In the spring of 1908, Knebel's fiancée, Ina von Grumbkow, came to Iceland in response to rumours concerning the circumstances of their disappearance - she did not believe they could vanish without a trace, and spent some time searching for her fiancé around Lake Askja. Her thoughts and words on departure describe the impression that this environment can have on travellers:
Few mortal men are consigned to such a majestic grave as the two who rest in this stately, bright mountain lake. Only kings need to dwell perpetually in their graves, where they are laid to earthly rest. Do those who rest in the golden sarcophagi of the Escarole Palace or the tombs of Egyptian pharaohs enjoy, in the human understanding, more serenity? Here, a peace of the greatest solemnity prevails on bright summer days and in the dark hours of winter - century after century.
Before Miss von Grumbkow left Askja, she and her escorts built a stone monument to commemorate the two men. The monument, which contains a guest-book, stands just north-west of the crater Víti.
Another memorial to the two scientists stands on the west bank of the lake, a cairn with a marble plate displaying engraved greetings from an Austrian research expedition that visited the area in 1950. The edifice stands at the place where the men are believed to have started their fatal journey, a walk of 3-4 hours from Víti.
Askja stands in the Ódádahraun lava field, a vast wilderness covering 5,000 km2, bounded by the marshland of Bárdardalsdrög in the west, the River Jökulsá á Fjöllum in the east and the barren plains of Mývatnsöræfi in the north. The desolate landscape is broken up by a number of small fertile areas.
The Dyngjufjöll volcanic zone cuts through the region, and the lava fields are the results of many eruptions there at different times during the past.