Hverfjall.  This prototype of a Tuff Ring was created during a 2-3 days’ eruption 2500 years ago.  The main reason for its creation is the constant presence of water, which prevented the distribution of the tephra over a large area.  The same applies to other Tuff Rings, such as Ludent and Hrossaborg.  Both Hverfjall and Ludent are parts of the volcanic system called Haedarspordskerfi. The Laxardalur Lava Fields shaped the landscape south and west of Lake Myvatn and all the way to the sea in the north.  The older lava field, 3800 years old, was created by the shield volcano Ketildyngja, and the younger one, 2300 years old, by the Haedarspordskerfi.

The recent tectonic and volcanic activities (1975-1984) are considered a part of a 2500 years long eruption period.  It started with The Hverfjall Period and continued with The Holseldar Period, Daleldar Period (where the geothermal power station is situated), Myvatn Period and Kroflueldar Period (the latest one).  The Krafla magma chamber reaches from 3 km depth down to 7 km.

The following geologically interesting places and areas are further described in the Travel- and Angling Guides:
Myvatn, Skutustadir, Ludent, Namafjall, Threngslaborgir, Hverarond, Hlidarfjall, Leirhnjukur, Viti, Hrafntinnuhryggur, Gjastykki, Sveinagja, Hrossaborg, Jokulsargljufur, Kelduhverfi, Tjornes.