Age: 2,800 years
Height: 660 ft (200 m)
Width: 1 mile (1.6 km)
Hverfjall, also called Hverfell, is a cone volcano in the north of
Iceland in the Mývatn area. Both names mean 'hot springs mountain'.
The volcano formed in a few days about 2,500 years ago. The
ejected lava was cooled almost immediately by water, making the
ring-shaped volcano almost entirely composed of tephra, ash and fine
grit.
The volcano is 312 meters high, has a crater with a
diameter of approximately 1 kilometer and is 140 meters deep. In the
center of the crater is a small ash mound. The crater wall can be
climbed via two not too difficult roads and a walk around it
provides beautiful views of Lake Mývatn. In order not to damage the
delicate structure of the volcano, the hiking trails must not be
left.
There are only a few volcanoes of this type on Earth: a
second one (Lúdent) is located next to Hverfjall; a third, somewhat
smaller one, Diamond Head, is located in Hawaii.
It formed around 2,500 years ago in huge water vapor explosions that were triggered when hot magma hit groundwater. The lava has solidified glassy due to water vapor. At the edge of a mighty column of water vapor, in which nothing could sink, volcanic loose material trickled down, forming this ring with a diameter of 1 km and a height of 90–150 m. Many of the innumerable layers were created by pyroclastic flows. The total volume of the ejected material was approx. 250 million m³.
There are only a few craters of this type on earth. The smaller Lúdent is located about 4 km south-east of Hverfjall. Other examples include Diamond Head and Koko Head in Hawaii, as well as small examples in the Fort Rock Basin, Oregon, USA.
The Hverfjall crater rim can only be ascended via two hiking trails, one from the northwest and the other from the south. It is not permitted to abandon the paths or seek alternative routes of ascent so as not to destroy the sensitive tufaceous geological formation.