Side‐scan sonar images of submarine landslides on the flanks of atolls and guyots

Geological studies of oceanic islands indicate that landslides play a large role in modifying the size and shape of islands. Sea floor mapping of the slopes of these islands shows that submarine landslides are common and widespread. Because surveys have concentrated on young volcanic islands (less than 28 My), little information is available about landslides on older atolls and guyots. Side‐scan sonar surveys are presented here of a Cretaceous age (100–70 My) guyot and an atoll. Both surveys show that landslides altering the carbonate caps are present on these features. Since the carbonate caps were formed long after volcanism ceased and the volcanic edifices had subsided, their modification suggests that landsliding continues to be a significant factor changing the shape and size of atolls and guyots. Early studies of atoll shapes indicate that few atolls are true ring reefs (about 5%). It is suggested that submarine landslides are the likely mechanism by which ring reefs are modified to irregularly shaped polygonal atolls.

Keywords:

• atolls
• guyots
• submarine landslides