The Earth Story

Tidally dominated deltas

This is a satellite photo of part of the Gulf of Papua captured by the USGS Landsat program in 1989. It shows two major river deltas – the large river on the western side is the Fly River and the river that splits into many channels in the center of the image is the Kikori River. Several other smaller stream channels sit in-between these two larger features.

These features are river deltas but they don’t look like the Nile River where it meets the Mediterranean Sea (origin of the term “delta). These rivers have many different channels and islands with a pattern that is almost perpendicular to the coastline.

The Gulf of Papua is blocked on several sides, isolating it from stronger waves in the open ocean, and it is a rainforest so the rivers don’t carry a huge sediment load. Consequently, the shapes of these deltas are dominated by the tides.

Tidally dominated deltas form when tidal energy is the main process that redistributes sediment. Sediment comes down the river channels, but not enough to overwhelm the force of the ocean. Every day, the tide goes out and comes back in, creating a motion path in and out from the shoreline. That in and out motion redistributes sediment, creating channels and islands that generally run perpendicular to the coastline as seen here.

When wave action is stronger, sediment can be redistributed alongshore, creating a wave-dominated delta. On the other hand, when sediment loads are so high that the waves and tides can’t redistribute all the dirt, a river-dominated delta is formed.

-JBB

Image credit: USGS/Landsat http://landsatlook.usgs.gov/viewer.html

Read more: http://bit.ly/1JFo52T

Thor's well While it resembles a bottomless hole draining the sea, and known colloquially as the 'drainpipe of the sea', this hole in the rock is only a few metres deep. The illusion results from a dangerous tidal phenomenon, and is best seen around high tide or during a storm, when waves pound in from the Pacific ocean onto this stretch of the Oregon coast. As the waves hit the rock, they spray upwards in a huge surge known as the Spouting Horn, before crashing into the hole and draining out. Be careful while visiting, as the waves can wash you into the maelstrom, with little chance of survival.  The Well is on Cape Perpetua, discovered by Captain James Cook in 1778 while seeking a route from the Pacific to the Atlantic, (the fabled Northwest Passage, that climate change may finally open up for us by melting the sea ice of the northern ocean. The area was long used by Native Americans, whose middens of empty mussel shells testify to their feasts of yesteryear. Loz Image credit: Bill Young http://www.amazingplacesonearth.com/thors-well-usa/ http://www.atlasobscura.com/places/thor-s-well https://roadtrippers.com/us/or/nature/thors-well-cape-perpetua

Peatlands: aquatic regulators This is a peat marsh or peatland found in Belarus. Peat marshes are locations dominated by soil layers known as, well, peat, a mixture of organic material in various states of decomposition, produced by centuries of plants growing and dying in the same location. Plants growing and dying on top of each other, like in this bog, will pile up thick layers of organic material mixed with large amounts of water. That soil will then serve as an anchor for additional plants to grow, stabilizing the water lines and the ecosystem over time. Those layers can then serve as homes for all sorts of additional plant and animal life, dependent on the stabilized peat layers. Peatlands are hugely important for mankind. They contain large amounts of stored organic carbon in them, so if they are damaged or destroyed, that carbon will rapidly release to the ecosystem and the atmosphere. Protecting peatlands therefore is a key step in fighting climate change. Peatlands in many areas are in fact under siege as they sit at areas where fresh water, like that found in a river, becomes stagnant. Draining peatlands can give water supplies useful for farming, electricity generation, and shipping, and can create land that people can build on. Every time this happens, the end result is going to be additional CO2 pumped into the atmosphere. These systems also serve as natural barriers against the weather. Peat bog soils can be up to 90% water, making them dense and capable of absorbing the force of storm surges and waves. Thick layers of peatlands can serve as natural protectors for cities upstream from hurricanes and typhoons, but only if they’re left in place. If the city upstream diverts the water that sustains them, the city may enjoy the water supply, but it also can put itself at greater risk from the oceans. -JBB Image credit: EGU Open Access http://imaggeo.egu.eu/view/614/ Read more: http://www.doeni.gov.uk/niea/biodiversity/habitats-2/peatlands.htm http://www.wetlands.org/Whatarewetlands/Peatlands/tabid/2737/Default.aspx http://www.peatsociety.org/peatlands-and-peat/what-peat