Namibia's spectacular coastline runs for over 1,500 kilometers (930 miles) along southwestern Africa, and is a mosaic of stunningly rich colors and textures. This true-color Terra MODIS image from April 2, 2005, shows one of the most spectacular portions of the coastline - the southern and central portions of the Namib Desert where giant orange sand dunes make ripples visible from space. The dunes can stand over 800 feet tall. Off the coast a bright turquoise-blue wash of color in the otherwise black southern Atlantic Ocean marks a sulfur eruption fed by nutrients in the Benguela Current.
Cold waters welling up from deep in the ocean replenish nutrients at the ocean surface and often result in a rapid increase in marine plant life, like phytoplankton, which in high-enough concentrations will turn the water blue-green. The phytoplankton live just a few days, and when they die their remains sink to the bottom of the ocean, where they build up in the mud on the coastal floor. Many types of bacteria help decompose the phytoplankton remains. Some of the bacteria consume oxygen in the process, and eventually all of the oxygen at the ocean floor is used up. At this stage, another kind of bacteria that use sulfur begin to thrive, and give off hydrogen sulfide gas as they further decompose the phytoplankton remains. The hydrogen sulfide gas periodically bubbles up from the ocean bottom, and when it encounters more oxygen-rich water near the surface, a chemical reaction occurs that transforms the sulfide gas into pure sulfur. In the first stages of the reaction, the sulfur appears white, and in this image creates a milky-green green tinge to the water. When the transformation is more complete, the plume will look very greenâ€”a mixture of the yellow sulfur and blue water.