AGU Press Releases and Images

December 2003


Complexities of Eruptive Processes at Mariana Forearc Serpentinite Mud Volcanoes and Implications for Serpentinite Melange Development

San Francisco - Detailed DSL120 side-scan sonar surveys and Jason2/Medea ROV observations of the summit areas of several serpentinite mud volcanoes on the eastern half of the Mariana forearc reveal vent dimensions and information about the size and dynamics of mud protrusions emanating from the vents. Some vents appear to be small (a few km in diameter), which suggests narrow conduits beneath the mud volcanoes. Other sites of mud flow emanation appear to be along fissures a few tens to hundreds of m long. New high-resolution bathymetry of the seamounts shows details of the seamount flanks that confirm multiple lobes of mud protrusions and show evidence of catastrophic collapse events, possibly associated with pulses of larger-volume fluid egress. The collapse events scour channels in the sides of the edifices and in some instances distribute large volumes of material about the base of the seamounts. The debris shed from the edifices can extend for tens of kilometers outward from the flanks of the edifices. The seamounts are clearly subject to large-scale episodic disruption. Some bear fault traces throughout the edifices. Shallow earthquake activity in the Mariana forearc is largely confined to the outer 100-km zone of faulting and serpentinite seamount formation. Fault zones in the outer forearc control canyons that probably channel debris from the seamounts toward the trench axis. The wide-spread distribution and reworking of debris shed from the mud volcano edifices and from fault-exposed serpentinite provides a model for the formation of complex serpentinite melange deposits in exotic terranes, such as the Franciscan of California.

For more information, contact Patricia Fryer, (808) 956-3146

Hawaii Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, HI 96822 United States

PDF of the Press Release is available here.

Click on the image to open a larger, complete image in a separate window.

This oblique view map of the southern Mariana Trench region shows the trench axis in deep purple (white cross marks the challenger Deep ~11,000 m). The shallow volcanic regions are in warmer colors. Areas of high data coverage from Hawaii Mapping Group side-scan sonar surveys show up in greater detail and surrounding areas with less well surveyed regions appear smoother. The islands of Guam and Rota are marked as well as the positions of several submarine volcanoes and the active mid-ocean spreading center in the new ocean basin (Mariana Trough) to the west of Guam. Two major fault traces are noted on the figure and have been the site of large magnitude earthquakes that have caused damage on Guam.

Map created by Nathan C. Becker/SOEST

These maps show the first detailed images of the Challenger Deep. Teh upper figure shows the ocean depths (blue=deeper). the numbers on the equal lines of depth (contours) are given in kilometers. Teh white cross indicates the position of the Challenger Deep (nearly 11,000 m). The lower figure is a side-scan sonar image of the seafloor near the Challenger Deep showiing faluts on the subducting oceanic plate, avalanches of debris shed fromthe fault scarps and mud volcanoes near the faults. The inner slope of the trench north of the trench axis (white line in bottom figure) is covered in debris that has tumbled down the southern edge of the overriding plate. The region is geologically very dynamic.

Image created by Nathan C. Becker/SOEST



For more information, contact Tara Hicks.


Last Updated Wed December 3, 2003. Maintained by Tara Hicks.

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