May 23, 2024

An astronaut aboard the International Space Station took this photo of the largest estuary in Madagascar. Today, more than half of this estuary is filled by the delta of the Betsiboka River, which flows northwest to the Mozambique Channel. The major port of Mahajanga lies on the coast at the top left of the image. Rice is the main crop grown in and around the delta.

Over the past 50 years, extensive areas of forest have been lost to logging and the expansion of agricultural land to support a rapidly growing population. This change in land cover has resulted in extensive soil erosion from hillsides within the Betsiboka catchment and other catchments throughout Madagascar. Eroded soil from the Betsiboka catchment enters the Betsiboka River and is transported downstream. After several decades of accelerated erosion, the delta now measures about 35 kilometers (22 miles) long and fills much of the estuary that was open to ships less than 100 years ago.

The delta, centered in this image, is a network of distributary channels between larger and smaller “tear-drop” islands. The iron-rich soils color the water in the distributaries a red-orange hue. Several islands appear dark green where forests have colonized the newly deposited land. Today, the delta and neighboring shorelines are home to the largest area of mangrove forests in Madagascar.

Compared with an astronaut photo taken 40 years ago (1984 inset), the 2024 photograph illustrates how the delta has continued to grow towards the Mozambique Channel. Sand banks that were covered by water at high tide have expanded and grown upward to become vegetated islands. Since 1984, two new vegetated islands have formed on either side of island “A,” one downstream of islands “B” and “C,” and three downstream of island “D.” A yet unvegetated sand bar is also visible downstream of island “D.”

Astronaut photograph ISS071-E-111691 was acquired on May 23, 2024, with a Nikon Z9 digital camera using a focal length of 210 millimeters. It is provided by the ISS Crew Earth Observations Facility and the Earth Science and Remote Sensing Unit, Johnson Space Center. The image was taken by a member of the Expedition 71 crew. The image has been cropped and enhanced to improve contrast, and lens artifacts have been removed. The International Space Station Program supports the laboratory as part of the ISS National Lab to help astronauts take pictures of Earth that will be of the greatest value to scientists and the public, and to make those images freely available on the Internet. Additional images taken by astronauts and cosmonauts can be viewed at the NASA/JSC Gateway to Astronaut Photography of Earth. Caption by Justin Wilkinson, Texas State University, Jacobs JETS Contract at NASA-JSC. - NASA Earth