August 30, 2021 - Lakes Rukwa and Malawi

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On August 27, 2021, the Moderate Resolution Imaging Spectroradiometer
(MODIS) on board NASA’s Terra satellite acquired a true-color image of
two lakes of the East African Rift Valley.

The Rift Valley began to form about 25 million years ago, as two plates
underlying the surface (Somalian and Nubian plates) started to pull
away from another plate (the Arabian Plate) in a slow process that is
called “rifting”. As the plates pull apart, the landscape undergoes
many changes, including volcanic activity, creation of hot springs,
lifting mountain chains, the appearance of geysers, and formation of
large, deeply depressed rift valleys. Today, the complex East African
Rift system that runs roughly 3,000 km (2,175 mi) from Ethiopia to
Mozambique.

Throughout the East African Rift, where the deep valleys fill with
water, large lakes have formed. Most of the lakes are endorheic—lakes
that do not empty into another body of water, such as a lake or ocean.
Some are saline, although most are freshwater. Each is unique. This
image contrasts the muddy waters of Lake Rukwa, in the northwest, with
the blue waters of Lake Malawi.

Lake Rukwa sits in southwestern Tanzania and covers an area of about
1,000 square miles (2,600 square km). With an average depth of about 10
feet (3 meters), and a brackish salinity, the muddy waters support the
third-largest fishery in Tanzania. It is also home to hippopotamus and
crocodiles—and the relationship between these creatures and the local
residents is not always easy. In December 2018, it was reported that
villagers on the shores of Lake Rukwa were living in fear following
frequent attacks by crocodiles. As recently as February 2021 reports
have made international headlines, when Xinhua reported that a
23-year-old Tanzanian man was seriously injured after a 2-hour fight
with a crocodile that attacked him as he bathed in the waters of Lake
Rukwa.

In contrast, Lake Malawi, located in the country of Malawi, is one of
the deepest lakes in the world, dropping to about 2,310 feet (704
meters) in the northern end. It covers about 11,430 square miles
(29,604 square kilometers). Lake Malawi is a “meromictic” lake, which
is a type of lake that has distinct layers of water that do not
intermix. In the case of Malawi, there are generally three layers.
Because the sediment of the lakebed is trapped in the lowest layer, the
upper layers can appear crystal clear. While hippopotamus visit parts
of this lake, the real fame for Lake Malawi is the great abundance of
fish species. Known as mbuna locally (“rockfish” in the Tonga
language), there are about 295 species that have been identified—and
may be many more as yet unidentified. Some species are very colorful,
with unique habits that make them popular as aquarium specimens.

Image Facts
Satellite: Terra
Date Acquired: 8/27/2021
Resolutions: 1km (490 KB), 500m (1.3 MB), 250m (2.9 MB)
Bands Used: 1,4,3
Image Credit: MODIS Land Rapid Response Team, NASA GSFC



https://modis.gsfc.nasa.gov/gallery/individual.php?db_date=2021-08-30

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