Rotten-Egg Gas Suffocating Fish Off African Coast

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As bacteria break down the diatoms in these dead zones, hydrogen sulfide gas is generated as a byproduct. The gas is trapped in the mud and builds up, until it is eventually released when the region is disturbed by surrounding forces.

The mud belt off the Namibian coast is at least 460 miles long (740 kilometers) and 47 miles (76 kilometers) at its widest point, off Walvis Bay. But until last year, no one had determined how widely the hydrogen sulfide gas emissions extended or how long they lasted.

"We still don't know much about the frequency of these events or what triggers the release of these gases from the mud belt, although there have been written accounts of this phenomenon dating back to the beginning of the 20th century," said Weeks, who noted that a massive release of the gas is occurring now. She and her colleagues are continuing their use of satellite images to study the gas emissions.

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