Hallmundarhraun is the largest
lava field of the
Borgarfiord district. It was probably created in the beginning of the
tenth century (Haukur Johannesson 1989), about half a century after
the first Nordic settlers came to the country.
The lava came through a few craters in the northwestern slopes of The
Two of them are still standing, but the rest has
obviously been covered with ice, because a few lava flows appear at
the edge of the ice. The lava flows are clearly of "The Shield
Volcano Type". The lava flowed across the
heaths between the glaciers and the Nordlingafljot River, down through
the valley along the mountain Strutur, all the way to the Hvita River.
The total length of the lava is approximately 52 km and
it hardly exceeds 7 km in width. It is mostly flat, of the Pa-hoe-hoe
type, and naked but for a few spots, where vegetation has started
growing near the end of the lava and where it is sanded, close to the
place of origin. The big caves, Stefanshellir, Surtshellir and
Vidgelmir, are situated in the narrowest stretch of the lava tongue,
close to its end.