silfra fissures on the mid-atlantic ridge at lake thingvallavatn, iceland

silfra mid atlantic ridge divergent tectonic plate lake thingvallavatn pingvallavatn iceland thingvellir national park plates lava field reykjavik vikings saga north american eurasian river unesco world heritage site landmark fissure rift attraction outdoors icelandic landscape water nature sky scenic tourism rock travel scenery view valley green sightseeing summer clouds golden circle fissures mid-atlantic