Long-term Observations On Mud-volcano Eruptions
LOOME proposes for the first time a detailed investigation of the temporal variability at an active gas emitting mud volcano covering the sequence of events before, during, and after an eruption. It also intends to analyze their effects on gas hydrate stability, seafloor morphology and the distribution and colonization patterns of benthic communities. A main goal of the project is the integration of existing technology to establish an autonomous non-cabled observatory for seafloor seismics, temperature and pore pressure, chemical profiling, sonar detection of gas flares, and hydrography of bottom water, together with the study of colonization patterns, community structure and biodiversity. The sensor systems and biological experiments will be integrated around a combination of deeply penetrating in situ temperature and geo-acoustic recording units, which will give an early warning of eruptive events.
This demonstration mission will be performed by a consortium of marine geologists, geophysicists, chemists and biologists from Norway, France and Germany, which support LOOME DM by external, national and institutional funds.
The Haakon Mosby Mud Volcano (HMMV)
After its discovery in 1989, the HMMV was investigated by various international expeditions and it has been regularly visited by several of the LOOME partners since 1999. The HMMV is ca 1,4 km in diameter (1.2 km2), but its seabed features reach only up to 15 m in height. The volcano sits on top of a giant gas chimney forming a window to the deep subsurface down to 3000 m bsf, from where warm methane-rich fluids are pressed upwards towards the cold seafloor. Under the outer rim at ca 500 m bsf, methane hydrates form a ring with a wall thickness of 200-300 m around the flat center. This hydrate-rich ring is lighter then the surrounding sediments, thus lifting the seafloor up to form a hummocky surface. It erodes patch-wise and intermittently at the surface, while growing at the base supplied by hydrate formation due to cooling rising fluids.
Bathymetric maps of HMMV. Left panel was recorded in 2003, right one with a 10 time higher resolution in 2006 by VICTOR ROV. Position of the temperature lance is indicated. Significant changes of seafloor bathymetry were observed at the edges of the flat central areas, especially in the north. Edy, Foucher (IFREMER) et al.
The seafloor habitats of the Haakon Mosby consist of several more or less concentric domains, which are related to patterns in fluid flow. By microbathymetry, using a sonar system on the ROV Victor, 2 highly detailed maps were produced, one in 2003 and one in 2006, concurrent to targeted video-mosaicking of large areas of HMMV. The elevated outer rim of ca 300 m width above the subsurface hydrate ring is colonized by symbiontic siboglinid tubeworms. In between tubeworm fields, patches of grey microbial mats occur where hydrates have eroded and warm gas rich fluids reach the seafloor. The transition zone between the central flat area and the tubeworm hills is covered by mats of giant sulfide-oxidizing bacteria, which also host a specific type of fauna. The center seafloor consists of greyish reduced muds, sometimes showing ripples, cracks and holes of cm to m diameter, which represent escape pathways for gas, fluid and muds.
This situation is not stationary. We have solid evidence that regularly a mayor eruption occurs. Therefore, we will position an observatory at the volcano, and record events using a variety of sensors during a period of 1 year.
We want to record the series of event that take place before, during and after an eruption. For this we ‘look’ in different directions: we listen to sound coming from the deep sediments, which are caused by mud movements. We expect that louder acoustics will preceed an eruption, but nobody has ever listened to a deep-sea mud volcano. We will record at the sediment surface changes in temperature and water chemistry, by sensor strings that cross the expected ‘hot spot’. When with these sensors something drastic is measured, the scanning sonar is activated and will measure the events in the water column. We hope this results in images of a methane plume, giving information on the amounts of gas released and the timing of the release.
Deployment of the observatory will occur in July 2009, recovery of instrument and data in August 2010. The observatory is currently under construction.