a round lava stone perfectly fitted into a small cavity in vulcanic rock, hvaleyri beach, iceland

backbone beach cavity concept conceptual crevice earth eruption firm fissures fit formation foundation fractured geology gravel grey ground hafnafjordur harmonize harmony hollow hvaleyri iceland icelandic land lava mainstay minerals nature pertinent position pyroclastic recess reykjavik rock round sediment solid still stone strength stress support surface tephra texture tuff volcanics volcano vulcanic