Sea-Floor Sunday #30: Submarine channels, deep-water Nigeria
In case you missed it, check out my post from last week about a relatively new online source of geoscience information and images, the Virtual Seismic Atlas.
One of the coolest parts of a 3D seismic-reflection survey is the very detailed map of the sea floor.
credit: Virtual Seismic Atlas (http://www.seismicatlas.org/)
This image is a perspective image of the sea floor in deep water offshore the Niger Delta. The most prominent features are the submarine channels cutting across the slope. Also note the narrow ridge that is roughly perpendicular to the channel trend (near the green-gray boundary by color). These ridges are compressional features caused by folding and thrust-faulting of the underlying sediment. The upper part of the slope on continental margin deltas such as the Niger will typically have extensional (i.e., normal) faults – in deeper water near the lower slope or base-of-slope, that updip extension is balanced by a compressional zone. Also note the scale of these submarine channel systems (scale bar on lower left) … these suckers are big.
Here’s the blurb about this image directly from the VSA site:
Sea bed images derived from 3D seismic for part of deep-water Western Niger Delta. The submarine canyons carve through ridges that are underlain by anticlines that represent part of the deep-water fold thrust belt. Various generations of canyons can be identified on the basis of cross-cutting relationships.
See the original image from VSA here.
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Note: All images above are property of Virtual Seismic Atlas (VSA). They are available for personal or educational purposes, but please visit their site and read terms of use [pdf] before doing so.
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Clastic Detritus 
As long as I have been in Geology, I have never heard of deep water fold and thrust belts.. a quick search shows these are really common on large continental scale deltas.
How do they form? Do all major delta’s have them?
What odd features.
CamArchGrad … they are very common on the world’s largest continental margin deltas … I will post some more information about them soon.
CamArch,
Delta fold and thrust-belts are common features in river deltas that develop on passive margins and in back-arc basins. The structural deformation style is rooted it two main attributes:
1) Sediment loading on the upper-slope of the delta.
2) Rheologically weak stratum within the delta (i.e. Ductile Evaporites and Shales).
The weaker strata owing to the increased sediment load, overpressure and becoming basal failure planes known as décollements. These décollements link the up-dip extension system to the down-dip (deepwater) compression system, accommodating the structural instability via gravity-driven failure of the delta.
Most geologists think of tectonic collisions as the only drive for compressional structures but gravity-driven compression is both common and happen to house some of the world’s most prolific hydrocarbon resources:
Gulf of Mexico (Mississippi Delta)
Niger Delta
Mahakam Delta
Rio San Juan Delta
Rhone Delta
Mackenzie Delta
Another common feature of deltaic gravity-driven systems are known as ‘diapirs’. Diapirs form when a weak stratum (ie Salts & Shales) becomes mobile and squeezes out of the down-slope compression system like tooth paste.
Great Blog and 3D Brian
Brantosaur … great answer, thanks! Make sure to check out seismicatlas.org, they got some cool images.
Can a tsunami occur off the Niger Delta coast?
Chima … thanks for the question … I honestly don’t know too much about the tsunami hazard for the western margin of Africa. Very generally speaking, the Atlantic coasts have a smaller risk than other ocean basins. Doesn’t mean there is no risk, just that the probability is smaller.
I searched around a little bit and found this report.
There is a lot of info in there, hopefully it answers your question or can lead you to getting more information.
Thanks Brian for creating this great blog and for posting the info on BHP Billiton’s Seismic-Atlas, they have some great teaching sets.
To answer Chima’s question: Yes, Tsunami can occur off the Niger Delta. Nevertheless Atlantic Tsunami are landslide related events not the Earthquake-Tsunami
A Tsunami is a displacement wave and can be triggered directly four ways:
1) Earthquakes (Indonesia’s “New Years Tsunami”: Jan 2004)
2) Landslides (Lituya Bay Tsunami, Alaska: July 1958)
3) Asteroid Impacts (Chixalube Impact: K/T event)
4) Volcanic Eruptions (Krakatoa: August 27th, 1883)
Or some combination of those four sources.
Tsunamis are most common in areas with active subduction zones and compressional tectonic margins (i.e. The Ring of Fire) as they have three of the four triggers for Tsunami (Earthquakes + Landslides + Volcanoes). Yet as the name implies Tsunami can be triggered by large scale slope failures in/into large water bodies without Earthquake involvement and these “Landslide-Tsunami” are what geologists and geophysicists are expecting/discovered evidence for in the Atlantic Ocean Basin.
Further information on Landslide-Tsunami:
S.N. Ward (2000). Landslide Tsunami. IN: Journal of Geophysical Research; Vol 1; No. 8; Pg 01-27.
Click to access single.pdf
Which models and discusses major submarine landslides in the Atlantic:
(1)The Storegga slide/Tsunami off the westcoast of Norway, in the North Sea
(2) The Norfork Submarine Canyon slide/Tsunami off the US eastern seaboard.
(3) And in the Pacific Ocean the Nuuanu Landslide-Tsunami off Oahu, Hawaii.
Landslide-Tsunami Propagation Images:
http://www.iris.washington.edu/about/ENO/iows/2_2003a.htm
Posted on the website of the Incorporated Research Institutions for Seismology (IRIS):
http://www.iris.edu/hq/
Images from:
S.N. Ward & S. Day (2001). Cumbre Vieja Volcano: Potential Collapse and Tsunami at La Palma, Canary Islands. IN: Journal of Geophysical Research. Vol. 28; Pg. 3397-3400.
C.L. Mader (2000). Mega-Tsunami. IN: Los Alamos Publication (LA-UR-00-1)
Click to access mader.tsunami.00.pdf
From:
C.L. Mader (1999). Modeling the 1958 Lituya Bay Mega-Tsunami. IN: Science of TZsunami Hazards. Vol. 17; Pg. 57-57.
Cheers to you both (Brian & Chima).
Thanks Brian for creating this great blog and posting the info on BHP Billiton’s Seismic-Atlas, they have some great teaching sets.
To answer Chima’s question: Yes, Tsunami can occur off the Niger Delta. Nevertheless Atlantic Tsunami are landslide related events not the Earthquake-Tsunami
A Tsunami is a displacement wave. Tsunami can be triggered directly via four events:
1) Earthquake – Tsunami (Indonesia’s “New Years Tsunami” of 2004)
2) Landslide – Tsunami (Lituya Bay, Alaska 1958)
3) Asteroid Impact – Tsunami (Chixalube Impact = K/T event)
4) Volcanic Eruption – Tsunami (Krakatoa)
Or some combination of those four sources.
Tsunamis are most common in areas with active subduction zones and compressional tectonic margins (i.e. The Ring of Fire) as they have three of the four triggers for Tsunami (Earthquakes + Landslides + Volcanoes). Yet as the name implies Tsunami can be triggered by large scale slope failures in/into large water bodies without Earthquake involvement and these “Landslide-Tsunami” are what geologists and geophysicists are expecting/discovered evidence for in the Atlantic Ocean Basin.
Further information on Landslide-Tsunami:
S.N. Ward (2000). Landslide Tsunami. IN: Journal of Geophysical Research; Vol 1; No. 8; Pg 01-27.
Click to access single.pdf
Which models and discusses major submarine landslides in the Atlantic:
(1) The Storegga slide/Tsunami off the westcoast of Norway, in the North Sea
(2) The Norfork Submarine Canyon slide/Tsunami off the US eastern seaboard.
(3) And in the Pacific Ocean the Nuuanu Landslide-Tsunami off Oahu, Hawaii.
Landslide-Tsunami Propagation Images:
http://www.iris.washington.edu/about/ENO/iows/2_2003a.htm
Posted on the website of the Incorporated Research Institutions for Seismology (IRIS):
http://www.iris.edu/hq/
Images from:
S.N. Ward & S. Day (2001). Cumbre Vieja Volcano: Potential Collapse and Tsunami at La Palma, Canary Islands. IN: Journal of Geophysical Research. Vol. 28; Pg. 3397-3400.
C.L. Mader (2000). Mega-Tsunami. IN: Los Alamos Publication (LA-UR-00-1)
Click to access mader.tsunami.00.pdf
From:
C.L. Mader (1999). Modeling the 1958 Lituya Bay Mega-Tsunami. IN: Science of TZsunami Hazards. Vol. 17; Pg. 57-57.
Brantosaur … your comments were put in my spam filter (probably because of all the links) and I just saw them now. Sorry about that.
Thanks so much for all the info and sharing your knowledge of landslide-related tsunami hazards. I’ll have to dig into those very soon.
Sorry for the replication Brian.
CamArchGrad: Fold and thrust belts are indeed very common on the toe-of-slope of most passive continental margins. They are gravity driven, unline “classic” fold and thrust belts like the Alps or the Carpathians that are driven by compression in areas of plate collions. A typical passive margin always has an area of extensional tectonics on the landward side, and obviously has to have an area of shortenning on the deepwater side. Think of it as one huge landslide.
Deepwater Nigeria a neat fold and thrust belt pretty cool to look at it on seismic (although it has some very lousy petroleum geology).
I recall a BHP paper that compared deepwater thrust belts to the plate-collion ones. There are some fundamental differences. I.e. the deepwater kind tends to consist of a densely spaced series of imbricate fault blocks, and lacks the typical ramp architecture that one finds in the Appalachians or in the Alps.
Chima Okenimkpe: Can a tsunami occur off the Niger Delta coast?
Yes. If a massive undersea landslide occurred on the shelf edge, it could trigger a tsunami wave. I believe this has happened once before.