Growth and destruction of Gran Canaria deduced from seismic reflection and bathymetric data

Abstract

The morphology and structure of the submarine flanks of Gran Canaria have been mapped using Hydrosweep swath bathymetry and high‐resolution reflection seismic data. The growth and destruction of the island has been characterized previously by three major periods of volcanic activity (16–9 Ma, 4.5–3.5 Ma, younger than 3 Ma) separatedby erosional intervals. Two major sector collapses along the west coast, inferred from the coastal morphology, are believed to have formed at the end of the shield‐building phase. One is characterized by a 19‐km‐wide reentrant along the northwestern coast that may have formed synchronously with the formation of the 20‐km‐diameterMiocene Tejeda Caldera. High sedimentation rates around Gran Canaria (>50 m/Myr) tend to cover and bury major landslide blocks. SSW off the island, several canyons continue seaward into a major sediment fan. A 9.5‐km‐wide volcaniclastic ridge in this fan is interpreted to represent deposits of the Pliocene subaerial Roque Nublo debris avalanche. We tentatively interpret the slope break at a depth of 600–800 m as the transition between subaerial and subaqueous chilled lavas at the end of the shield‐building phase. The subsidence caused by the volcanic load (30,000 km3) on the lithosphere may thus amount to no more than 800 m. Several canyons on the island can be traced down the submarine flanks to a depth of 3.5 km, indicating that at least deeper portions below the level of subsidence were eroded by mass flows continuing seaward from the subaerial canyons. Four submarine volcanoes were identified west and northeast of the island.