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CD 166: Exploring underwater avalanches offshore Morocco


About the cruise...

On Oct 26th 2004 an international team of marine scientists will leave Lisbon for the start of a new research cruise on the British ship, RRS Charles Darwin (left). The scientific team, representing the UK, Spain, Germany, Russia, Greece, Italy and Portugal, will be led by SOC's Chief Scientist Russell Wynn and University of Aberdeen's co-Chief Scientist Dr Bryan Cronin.

Where are we going?

The team will sail from Lisbon in Portugal, southwards towards NW Africa. The area the team are studying is located several hundred kilometres offshore Morocco, between Madeira and the Canary Islands. This part of the seafloor is known as the Agadir Basin, and lies more than 4km below the sea surface. Carving its way down to the Agadir Basin from the Moroccan coastline is a deep ravine known as the Agadir Channel (see the map, right). The Agadir Basin and the Agadir Channel are the two areas under investigation on this cruise.

Map of the cruise area
(Click to enlarge)

What are we investigating?

The main aim of the cruise is to take sediment samples (cores) from the deep Agadir Canyon and Basin. The water is over 4 km deep in this region, and the work area is several hundred kilometres from the Moroccan coast to the east and the volcanic Canary Islands to the south. However, earlier investigations in this areas have shown that the seafloor sediments contain Moroccan beach sands, volcanic lava fragments from Tenerife, and even pieces of wood!

This material was transported down to the deep sea by giant underwater avalanches (composed of a turbulent mixture of water, sand and mud), that originate as landslides in shallower water close to land. These underwater avalanches then travel downslope at high speed through canyons and channels until they reach the flat basin floor. Most of their sand and mud is then dumped, smothering huge areas of seafloor and destroying all life. By studying the deposits left behind by these catastrophic events, scientists can work out where they come from, how often they occur, and whether they are capable of generating potentially damaging tidal waves that could effect coastal towns and villages in the region. They can also see how quickly deep-sea organisms can re-colonise the seafloor after being exterminated. 

Find out more about the geology of the Agadir Canyon and Basin
Find out more about sedimentary processes in the deep sea

Why do we need to know about this?

This cruise is sponsored by a number of oil companies, and they have a keen interest in this reasearch for two main reasons. The first is that the Agadir Basin is very similar to the geology found deep in the Gulf of Mexico, one of the largest hydrocarbon provinces in the world. The oil reservoirs (sediments and rocks that contain oil) deep below the seafloor in the Gulf of Mexico can be imaged using modern seismic techniques, but to drill a hole through the seafloor down to these reservoirs to actually look at the rocks can cost 70 million dollars - a very expensive process! By studying modern equivalents of the Gulf of Mexico, such as the Agadir Basin, both the scientists and oil companies can better understand the sediment types in this sort of basin and can get a better idea of where the best oil reservoirs might be found.

The second reason is that there is currently a lot of gas and oil exploration on the Moroccan margin near the head of the Agadir Canyon. Understanding recent sediment activity in the canyon and how sediment moves down to the deep ocean from the continental shelf is important for assessing hazards to seafloor installations such as oil rigs and wells. This helps the petroleum industry to use the most up to date and accurate information to ensure safe and efficient working practices in deep water.

From a purely scientific point of view, studying the Agadir Canyon and Basin is important in understanding the history of landslides and turbidity currents in the region. The Canary Islands, just to the south east of the study area, are volcanic in origin and prone to landslides occurring on their flanks. Although large landslides on the Canary Islands are rare events (one in every 100,000 years) it is still important to study them to try and predict when the next one might happen and whether it would trigger an event such as a tsunami (giant tidal wave).

[see BBC News Online article about Canary Islands landslides]

Find out more about...
The geology of the Agadir Canyon and Basin
How TOBI works and what sidescan sonar images look like
How we take sediment cores from the deep sea
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© Challenger Division for Seafloor Processes
October 2003
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