Delta on EARTH Magazine

Greenland's growing deltas: Combining historical and modern imagery to decode change in a telltale Arctic landscape

Fri, 09 Feb 2018 14:50:54 -0500

The coast of Greenland has more than 100 pristine deltas formed by rivers draining from the Greenland Ice Sheet into the sea, interspersed amid the coast's irregular geometry of fjords and icy bays. Credit: Anders Anker Bjørk.

Enormous quantities of fine sediment, sand and rock are carried downstream by rivers flowing off the Greenland Ice Sheet. Where these rivers meet the ocean, they deposit the sandy, coarse part of their sediment loads, forming textbook fan-shaped deltas. Credit: Nicolaj Krog Larsen.

Greenland’s rivers are impressive, with fast, powerful flows of turbulent, milky waters descending from glaciers of the Greenland Ice Sheet, which loom only a few kilometers upstream. Enormous quantities of fine sediment known as “glacier flour,” as well as sand and rock are discharged into and carried downstream by these rivers. The grinding action of the sediment-laden torrents is formidable and carves beautiful smooth sculptures in the solid granite bedrock. From the riverbank, the noise is overwhelming as the loud crashing of the turbulent water flow combines with a rumbling undertone from rocks colliding with the river bottom.

Travels in Geology: Tracking African animals and deranged drainages across the Kalahari

Fri, 19 May 2017 12:03:03 -0400

The local name for Victoria Falls translates as "The Smoke That Thunders." Credit: Lon Abbott and Terri Cook.

After landing in Windhoek, Namibia, on the western edge of the Kalahari Desert, our family embarked on an African adventure with two exhilarating objectives: to see iconic African animals in the Okavango Delta, a major river delta in the middle of the dry Kalahari, and to view the thundering Victoria Falls, a day’s drive from the delta on the desert’s northeastern side. Most tourists consider these two magnificent UNESCO World Heritage sites to be wholly unrelated. But to a geologist, they are inextricably linked via major hydrologic changes that have swept across the region in response to both subtle tectonic movements and major Pleistocene climate fluctuations.

Measuring rising seas is tricky in deltas

Thu, 19 May 2016 16:38:36 -0400

Researchers used an experimental basin filled with water and sand-, silt- and clay-sized sediments to mimic natural deltas and study the formation and preservation of stratigraphic records. Credit: Kyle Straub.

Earth’s stratigraphic record offers a patchwork diary of how different parts of the planet have formed and changed over time. Some of the most extensive pieces of the stratigraphic record are found in deltas, making them ideal places to look for long-term chronicles of Earth’s history, as well as clues to future changes to our coastal landscapes.

Sinking sediment in deltas is as important as swelling seas

Wed, 25 Sep 2013 13:57:34 -0400

Landsat 7 view of the delta of the Nile River where it empties into the Mediterranean. NASA

Sea-level rise due to melting ice is a common worry in coastal areas. But the sea-level story is much more complicated: What lies below the surface — sediment, and the rate at which it compacts — is also an important consideration, especially in deltas.

Raising California's Sinking Delta

Thu, 05 Jan 2012 06:41:58 -0500

Over the past century and a half, the river delta that provides Central and Southern Californians with drinking water and farmers with productive cropland has sunk about two and a half centimeters each year. Some of the delta’s islands now lie more than six meters below sea level. Two thousand kilometers of aging levees keep them dry for now, but as the land sinks, the pressure on the levees grows. Researchers at the U.S. Geological Survey in California have uncovered a way to rebuild the delta and sequester carbon in the process. Now, with a $12.3 million grant from the California Department of Water Resources, they will test their strategy on a much larger scale.