Global Volcanism Program | Image GVP-06037
This north-looking view along fissures cutting Iceland's Krafla volcano illustrates crustal spreading processes where the Mid-Atlantic Ridge rises above sea level. The prominent horst-and-graben structures seen here are the result of repeated episodes of extensional rifting during which crustal blocks moved east and west, perpendicular to the line of faults. Crustal rifting was occurring at the time of this September 1984 photo; steam rises at the upper left from an active eruptive fissure.
Photo by Michael Ryan, 1984 (U.S. Geological Survey).