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Submarine Canyons: Applying Geomorphometry to understand their Evolution

Final Report Summary - CAGE (Submarine canyons: applying geomorphometry to understand their evolution)

The principal results of the CAGE project include the following:

(1) The role of submarine mass movements in canyon evolution: A study of the Cook Strait canyon system offshore New Zealand showed that landslides can be the most efficient process removing material from canyons and can affect up to 25 % of a canyon's surface. Landslides control flank erosion, lateral extension and tributary development, allowing the canyon to evolve into a dendritic network. They also transfer material to the canyon floors. Landslides in canyons are triggered by loss of support, associated with canyon bed incision, and earthquakes. The influence of landslides becomes more significant as the canyon matures. Numerical modelling of tsunami generation and propagation indicates that landslides in the Cook Strait canyon system constitute a realistic hazard to Wellington coastal communities and infrastructure.

(2) Submarine canyon initiation and evolution in passive margins: By investigating the south Ebro Margin (Mediterranean Sea), the researcher demonstrated how canyons in passive, progradational margins develop into geometrically self-similar systems that approach steady state and higher drainage efficiency. He documented how a first-order gully can develop into a mature shelf-breaching canyon and, finally, into a canyon-channel system via coupling of gravity flows and slope failures. Canyon activity is pulsating and closely linked with low sea-levels and paleo-river sediment deposition during glacial periods. Connection of the canyon with a paleo-river changes canyon dynamics significantly, triggering the development of a canyon-channel system. Canyon morphology in a passive margin is shown to be maintained over the course of more than one fall and rise in sea-level.

(3) Development of a multi-method habitat mapping technique: The researcher developed a semi-automated, geographic information system (GIS)-based methodology to map the distribution of seafloor habitats using high-resolution multibeam echosounder (MBES) data. Morphometric attributes, the bathymetric position index and geomorphometric mapping were used to classify the seabed into five elementary morphological zones. Subdivision of the seafloor into four predominant types of composition was carried out using roughness estimation and supervised classifications of morphometric derivatives of bathymetry and textural indices of backscatter; these were based on seafloor imagery and samples obtained from training stations. As the European Union (EU) Member States have embarked on the mapping of their coastal waters in fulfillment of their obligations under the Maritime Strategy Directive, this approach can provide an efficient and cost-effective technique to map and manage coastal and deep waters.

(4) Submarine canyon evolution in sediment-undersupplied margins: Canyons incising sediment-undersupplied margins are often considered inactive, relict features without risk to human activities and installations. Data acquired from the Malta-Sicily Escarpment during the CUMECS cruise provide evidence of recent shallow landslides, exposed and buried channels draining into a densely-gullied canyon head, contouritic deposits and deep-water coral communities in the canyon head. This indicates that canyon processes have been active recently and are likely driven by seismicity and deep ocean circulation in the region.

(5) Submarine canyon initiation and evolution in active margins: canyon topography in active margins such as the Hikurangi margin, offshore New Zealand, fails to reach steady-state because of continuous adjustment to perturbations associated with tectonic displacements and base-level change. Such transient adjustments migrate up the canyon and are revealed by multiple knickpoints and convex longitudinal profiles. In comparison to passive margins, active margin canyons are steeper, asymmetric, have higher gully and landslide densities, and show more recent and frequent evidence of gravity flow activity.

(6) The role of gully erosion in submarine canyon evolution: Gullies are small, straight and shallow channels that are widespread in submarine canyons. In Micallef and Mountjoy (2011), the researcher had shown how gullies may be initiated by unconfined, downslope-accelerating gravity flows. In CAGE, collaboration with researchers from the University of Barcelona has extended this study by identifying two types of gully morphologies:

(i) rim gullies, which are the main process responsible for canyon head growth and across-flank transport of material from the continental shelf; and
(ii) toe gullies, which are the morphological expression of the rejuvenation of rim gullies and the canyon itself.

At community level, the CAGE project and its results have a number of direct implications:

(1) By developing high quality scientific methods, improving the scientific knowledge base for the marine environment, supporting the deep-sea research community, and structuring fragmented data from various European studies, the project enables the EU to play a key role in international ocean governance by designing and optimising policies in line with the best available scientific evidence. The timing of CAGE is excellent because the EU is in the process of implementing its Integrated EU Maritime Policy, a section of which focuses on marine environmental degradation, and of implementing its Marine Strategy Framework Directive (2008). The CAGE products will also facilitate conservation of ecosystems and the sustainable management of natural resources, consolidating the global commitment of the EU in this regard.

(2) By identifying the dominant geological processes driving canyon evolution and their spatial organisation, CAGE allows understanding of the effects of canyon processes on the distribution and abundance of benthic ecosystems, reduce potential damage to seafloor infrastructure and coastal communities through improved geohazard assessment and enhance hydrocarbon assessment by developing analogues of old formation both on land and offshore.

(3) The Malta-Sicily Escarpment is one of the least studied regions in European seas. Through the CUMECS cruise, CAGE generated new data that will have a significant impact on fundamental deep sea research in the central Mediterranean Sea and that will be useful to the government of the Maltese Islands to better understand manage its marine geological and biological resources.

(4) The researcher has also organised and integrated dispersed geophysical data sets acquired within the framework of previous EU-funded projects, addressing the need for data management and integration within the European Research Area (ERA). He also developed quantitative techniques that are useful for submarine canyon investigation, habitat mapping and delineation of marine protected areas. These tools are universally applicable and have been widely disseminated; this transfer of knowledge will bridge existing technological divides and enhance European scientific excellence.

(5) The mobility associated with CAGE was fundamental to the career development of the researcher because he was able to develop and expand his links with partners in Europe and around the world. This will allow the ERA to take a leading role in international research initiatives and to have access to increased financial resources. The project was also an opportunity to build an international collaboration between the University of Barcelona and the University of Malta, where the researcher has conducted his undergraduate studies and where he is planning to continue his research after the conclusion of the project. This collaboration has enhanced the research profile of the University of Malta and transformed it into an important player in the ERA.

(6) The EU will benefit from the scientific and policy driven outcomes of CAGE and from the enhanced skills of the researcher. The EU is an important player in the research of submarine canyons, as exemplified by funding of related research projects as part of the Framework VI and VII programmes. The project has extended European research capabilities and expertise because the methodology developed can be applied to a larger class of geoscientific problems, and the results will be useful in the study of submarine canyons around the world. The EU's scientific excellence has also been improved with the publication of the outcomes of CAGE in high profile scientific journals.

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