The Earth Story

Seaweed Farms?

Seaweed is practically a staple food in coastal East Asia, and you'll find it in restaurants and supermarkets across the globe. Today, 90% of it comes from seaweed farms. This image, captured by NASA's Landsat 8 satellite, shows seaweed farms off the coast of South Korea.

Each dark stripe or block is a 'field' of seaweed. These 'fields' consist of parallel rows of stakes connected by long ropes, with periodic shorter ropes hanging down towards the sea floor. Each one of these hanging ropes has seaweed growing from it. It's worth taking a look at the full resolution image, to see the incredible extent of these seaweed farms - be sure to zoom in and scroll around (http://goo.gl/Lly2t7).

Seaweed farming, like all farming, causes a degree of environmental disruption, mostly from clearing mangrove swamps or existing sea-grass beds. However, these damaging practices are usually actively discouraged, as they reduce water quality, and damage the seaweed crop. In fact, seaweed farming is pretty good for the environment, as it goes. They don't require the use of fertilisers, they don't need a fresh water supply, and they provide valuable breeding grounds for a wide variety of fish and invertebrates, which are good for the whole marine ecosystem. They can even be used to 'soak up' damaging excess nutrients from terrestrial farms which flow down rivers into the sea.

I think I'll have Sushi tonight...

Image Credit: http://goo.gl/qU0bQA

Further Reading: - NASA Earth Observatory Post:http://goo.gl/qU0bQA - Seaweed Farming in the USA:http://goo.gl/VlQEuQ - Seaweed farming to fight climate change:http://goo.gl/ErYl4z

seoul_nightview 

6 peaks of Ulsanbawi (also called Ulsan Rock), some mesozoic aged granites in  Seoraksan National Park, South Korea

Birth of Subduction between Japan and Korea

The East Sea (also called the Sea of Japan) is an area composed partially of oceanic crust, with stacks of sedimentary piles on top of that crust and thick piles of igneous rock accumulated at the bottom. This sea opened as what geologists call a back-arc basin – an area of ocean crust that forms when a volcanic arc is literally pulled away from a continent. In this case, Japan was pulled farther away from the rest of Eurasia on a complex series of faults, allowing igneous rocks to come up and fill in the gaps to create oceanic crust.

However, back-arc basins don’t always last that long. Often, the force that pulls them apart – a very fast moving subduction zone – slows down, and the basin that opened turns around and starts closing. Today, this is happening to the East Sea. As shown in the maps and cross section from this just-published paper, the eastern side of the East Sea, the Japan side, now hosts a thrust fault big enough to create a magnitude 7.7 earthquake in 1983.

This paper studied the Korean side of the East Sea using seismic imaging, and found that the same type of structures exist on that side. There are developing thrust faults and folds forming beneath the Korean peninsula, which so far in recorded history have produced earthquakes with magnitudes up to 5.1.

The faults on the Korean side of the East Sea are not as well developed as those on the Japanese side, but basically the same thing is happening on both sides; thrust faults are beginning to fold and break up the crust. At some point, one, if not both of these sides will likely develop into a full subduction zone, with the crust beneath this Sea pushed down into the mantle. Which side will develop into a fully active zone is unknown, but in both cases on the sides of this Sea, scientists have the ability to see the faults that form as a new subduction zone develops. That’s pretty cool, as how exactly subduction zones develop is a subject geologists are still working to understand today.

-JBB

Image credit and original paper: https://doi.org/10.1130/G40305.1

*Note – there is dispute over whether the Sea of Japan or the East Sea is the proper name for this area on Earth. This paper specifically refers to this area as the East Sea, meaning that for the purposes of this paper’s editorial office that name has been judged as sufficient and accurate. I have adopted the same naming system here solely because that naming system was used in the original paper.

Ice climbing, Pandae Ice Park, Korea