Trolladyngja is a
hyaloclastite mountain to the north of Ridge Nupshlidarhals. Between
this ridge and shield volcano Trolladyngja is the shield volcano
Graenadyngja with the area Sog in-between. Shield Volcano Trolladyngja
has two main hyaloclastite peaks, 393 and 374 m. high. It also contains
major central volcanoes to the south and north. Its lavas have run from
there to create various lava fields such as Afstapahraun. There is
great thermal activity within this area.