Temporal dynamics of mid-ocean ridges and submarine volcanoes

1998 Projects

Project 4

Temporal dynamics of mid-ocean ridges and submarine volcanoes

Principal Investigator: Debra Stakes

Co-investigators: Dave Clague, Jennifer Reynolds, Michael Begnaud

Collaborators: Jim McClain, Karen McNally

The creation of oceanic crust is volumetrically the most important process in Earth’s geology. About 80 percent of all volcanic activity occurs at the mid-ocean ridges. The continual circulation of water through hydrothermal systems at the ocean floor has kept seawater chemical concentrations within ranges that have allowed life on the planet to persist for at least two billion years. To understand the linkages between the volcanic, tectonic, hydrothermal, and biological systems at all stages of crustal processes is the goal of this project. The investigative efforts fall into two main categories: collecting and comparing rock samples from various locations that span from the oldest crust accessible to recently formed crust, and measuring ongoing seismic and volcanic events with seafloor instruments left in place for extended periods. The project elements are:

P4A Submarine volcanic processes of the Hawaiian Islands and Pioneer, Taney, and Davidson seamounts—Ocean crust is formed at mid-ocean ridges and oceanic volcanoes by a complex series of melting and cooling events. These episodes leave a geochemical "imprint" in the make-up of the crustal rocks. Unraveling the events that formed such rocks provides insights into the processes occurring in Earth’s mantle, the source of the molten magma that wells up to feed volcanic eruptions. In some instances submarine volcanic activity produces chains of volcanoes, as in the mid-Pacific, where the Hawaiian Islands are the above-water representatives of a 6,000-kilometer (3,700-mile) chain of extinct volcanoes stretching to the northwest. Eruptions and the internal movements of magma within active oceanic volcanoes trigger earthquakes and landslides, which reshape the volcanoes. Under this sub-project, MBARI geologists will investigate several areas to gain a better understanding of the complex processes that modify ocean crust and oceanic volcanoes:

Offshore of Central California—On seamounts believed to have formed in the same era as the San Andreas fault system, researchers will use the ROV Tiburon to collect rock samples and survey the seamounts and their structures. The samples will be analyzed for their compositions, ages, and alterations made by past hydrothermal activity. Researchers are interested in knowing whether the seamounts were ever above sea level, and why some of them have very large calderas (volcanic craters formed by explosive eruption or collapse of the volcano). From these findings institute scientists hope to better reconstruct the history of the continental margin off Central California.

Hawaii—The extensive study of sub-aerial (above sea-level) volcanoes has revealed much about their evolution after they have built an edifice large enough to emerge from the sea. However, much less is known about processes of earlier, submarine volcanic stages and how they compare to above-water volcanic stages and to mid-ocean ridges. Institute studies off the island of Hawaii will shed new light on these questions. In February, as part of the first leg of MBARI’s survey project (under Project 11), researchers will conduct a sidescan sonar survey of the underwater flank of Kilauea volcano. Geologists will use the resulting maps and other larger-scale maps for comparing Kilauea’s underwater structure with the much-better-studied terrestrial portion of the volcano and with mid-ocean ridges. MBARI researchers will participate in two other research cruises on Kilauea’s submarine rift zone, using a submersible to collect lava samples and high-resolution sonar information to map the depths and details of lava flows, vents, and other features. In addition, they will use a human-occupied submersible to survey areas of Loihi, the youngest volcano in the Hawaiian chain. Laboratory analysis of lava samples from past submersible dives on Loihi continues. The findings thus far have raised intriguing questions about processes, such as submarine explosions, which researchers previously considered unlikely to occur on deep submarine volcanoes.

Other locations—Past research on submarine volcanic activity from other locations is being completed. These projects include studies on seamounts in the Austral Islands region (near Tahiti) and analyses of samples from the Hawaiian Islands and the Gorda Ridge and East Pacific Rise, both parts of the global mid-ocean ridge.

P4B Study of altered oceanic crust and hydrothermal precipitates from mid-ocean ridges and ocean islands—The formation of oceanic crust is intimately related to cooling and modification of the crust by seawater. Mapping the distributions of minerals known to be formed under high temperatures identifies permeable zones in the rock where hydrothermal processes occur. Solid compounds precipitate out of the hot vent fluids as they flow into the cold seawater. The make-up of the precipitates reflects variations in the temperature and chemistry of the venting fluids. Analysis of rocks of various ages and locations collected by MBARI researchers should reveal much about these key processes.

In March institute geologists will make an expedition to the Atlantis Bank in the southwest Indian Ocean, where one of the best exposures of the lower oceanic crust exists. The crust formed at a mid-ocean ridge and was transported away as newer crust displaced it. Over the ages fractures formed paths for water to seep in and buoy the crust up to relatively shallow depths (700-2,500 meters). Institute scientists will collect samples at Atlantis Bank with the MBARI multi-core rock drill mounted on the Canadian ROV ROPOS.

Samples to be collected from seamounts off the Central California Coast (P4A) will represent quite different geologic settings and eras. Davidson Seamount is believed to be a failed mid-ocean ridge; together with Pioneer and the Taney Seamounts, it is tied to the evolution of the San Andreas Fault system. The seamounts have resulted from volcanism superimposed on crust from mid-ocean ridges. Deciphering past hydrothermal activity at these offshore sites will tie in to ongoing regional geologic studies at MBARI.

The rocks from the Atlantis Bank and Central Coast offshore seamounts also will be compared to basalts (volcanic rock) from Monterey Canyon and samples from cruises to the Juan de Fuca Ridge, an area of very active underwater volcanism and hydrothermal venting. The comparative studies will help researchers address large questions such as how much oceanic crust is chemically altered by hydrothermal activity. The findings will also contribute to models that attempt to describe the flow of heat in Earth’s outer layer.

P4CBenthic observatory on the Juan de Fuca Ridge—To lay groundwork for the long-term objective of establishing a seafloor observatory on the south end of the ridge, geologists will begin by collecting data for a geological map of fine-scale bathymetry on a section of the ridge. A large-scale, combined side-scan/bathymetric survey will provide continuous data of the entire southern Juan de Fuca Ridge and the western half of the adjoining Blanco Fracture Zone. This will be followed by a higher- resolution survey that will be centered over the most hydrothermally active area of this ridge segment. MBARI researchers will also deploy a small number of seismic instruments in collaboration with NOAA. Ultimately, the goal is to join with NOAA and other agencies in setting up a series of instruments and samplers that will continuously monitor events (such as earthquakes and magma movements) related to ocean crust formation and sample seafloor fluids that have been modified by interaction with cooling crustal rocks. The goal of the 1998 efforts is to determine the kinds of instrument systems that should be developed and the optimal design for the seafloor observatory.

P4D Margin seismology system development— During 1997, in the MOISE (Monterey Ocean Bottom International Experiment) MBARI scientists and collaborators successfully deployed a variety of seismic instruments in Monterey Canyon for extended periods, which registered many regional and distant earthquakes. In 1998 they are developing new technologies for long-term observations; the permanent deployment of short-period seismometers is the highest priority. These seismometers, which record local events with high accuracy, are placed in coreholes drilled by an ROV. Up to five instruments will be placed in seafloor locations to provide seismic signals from several stations, which will improve the accuracy in determining earthquake locations and regions of stress release. These sensors will register microseismicity—signals from minor earth movements that reveal aspects of the mechanisms of earthquake faults, such as the angle of the fracture and the way fault movement occurs. From this, scientists can glean much about the underlying structure of the canyon and the behavior of active faults and pinpoint which faults might generate potentially damaging earthquakes. The seafloor seismic data will be combined with earthquake data from land-based stations. Used together, the records will assist scientists in determining more precisely the locations of both offshore and onshore earthquakes. A better understanding of the fault systems of the canyon will also likely shed light on the patterns of fluid flow from the seafloor and the occurrence of landslides that reshape the canyon—both intimately linked to the faults.

Next: Marine microbial ecology

Last updated: 23 November 2005