GeoLog

watershed

Imaggeo on Mondays: Ice forming on Chesapeake Bay

Imaggeo on Mondays: Ice forming on Chesapeake Bay

Sandwiched between the U.S states of Mayland, Delaware, Pennsylvania, New York State, the District of Columbia and Virginia, lies Chesapeake Bay, the largest estuary in North America. It is of huge ecological importance: “the bay, its rivers, wetlands and forests provide homes, food and protection for countless animals and plants”, says the Chesapeake Bay Program. Up to 150 major rivers and streams feed into the bay’s watershed.

Geologically speaking, Chesapeake Bay isn’t very old. As recently as 18,000 years ago the bay was covered by dry land. Global sea levels were up to 200m lower than they are at present and the last of the great ice sheets to cover America was at its peak. The rivers which flowed along the east of the continent had to cut valleys in what is now the bay bottom, to reach the continental shelf, and drain out to sea.

Fast forward 8,000 years and rising global temperatures caused the ice sheets to melt rapidly. Global sea levels started to rise, flooding the continental shelf and coastal areas, which now make up the modern-day estuary.

The process was helped along by a remarkable, much older geological feature. During the late Eocene, 35 million years ago, the Atlantic margin of the U.S was struck by a 3.5 km bolide (an asteroid or meteorite). The impact crater is located about 200 km south of Washington D.C., buried below 300 -500 m of sediments in Chesapeake Bay. Though the crater didn’t form the estuary, it did create a long-lasting depression in the area which helped determine the location of the bay.

Landsat satellite picture of Chesapeake Bay (centre) and Delaware Bay (upper right) – and Atlantic coast of the central-eastern United States. Credit: Landsat/NASA. Distributed by Wikimedia Commons.

Further reading

The Chesapeake Bay Bolide Impact: A New View of Coastal Plain Evolution: USGS Fact Sheet 049-98.

Chesapeake Bay Program

Landsat Images Offer Clearer Picture of Changes in Chesapeake Watershed (Nasa Landsat Science)

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

Imaggeo on Mondays: Emerald Moss

Imaggeo on Mondays: Emerald Moss

The high peaks of the Tien Shan Range, one of the biggest and largest mountain ranges of Central Asia, conjure up images of snowcapped peaks, rugged terrains and inhospitable conditions. Yet, if you are prepared to look a little further, the foothills of these towering peaks are a safe haven for life. Bulat Zubairov, a researcher at Humboldt University, takes us on a journey of discovery to the Ile-Alatau National Park in today’s Imaggeo on Mondays post.

This photo was taken in the Ile-Alatau National Park, approximately at this point: 43° 9’31.81″N, 77° 5’47.36″E. The National Park is located on the northern slopes of Ile Alatau (Zailiysky Alatau) mountain range, which is a part of the Tien Shan Range and it is a main recreation zone for people who live in Almaty (the biggest city in Kazakhstan).

The photo was taken in a small watershed – an area or ridge of land which separates two bodies of water – where a small river flows. The upstream section of the watershed dries up periodically over the summer periods.

Reflecting the rich fauna and flora of the Ile-Alatau National Park, more than 100 species of mosses can be found in this area in a wooded zone. They play a significant role in regulation of water balance of the region, preventing soil erosion, supporting special types of biocenosis and promoting biodiversity conservation. Being one of the indicators of ecosystem condition, mosses also play a key role in monitoring and assessment of current changes in ecology of the region, especially taking into account ever-growing anthropogenic pressures. All this shows the relevance of efforts aimed at researching of such a beautiful and such important part of nature as mosses.

By Bulat Zubairov, PhD student at Humboldt University in Berlin

If you pre-register for the 2016 General Assembly (Vienna, 17 – 22 April), you can take part in our annual photo competition! From 1 February up until 1 March, every participant pre-registered for the General Assembly can submit up three original photos and one moving image related to the Earth, planetary, and space sciences in competition for free registration to next year’s General Assembly!  These can include fantastic field photos, a stunning shot of your favourite thin section, what you’ve captured out on holiday or under the electron microscope – if it’s geoscientific, it fits the bill. Find out more about how to take part at http://imaggeo.egu.eu/photo-contest/information/.