This satellite image of the summit of Mauna Loa overlaid with contour lines helps illustrate why volcanic emissions from the summit rarely reach the observatory where atmospheric carbon dioxide is measured.
Emi Koussi is a high volcano that lies at the south end of the Tibesti Mountains in the central Sahara in northern Chad. The volcano is one of several in the Tibesti massif, and reaches 3415 m in altitude, rising 2.3 kilometers above the surrounding sandstone plains. The volcano is 65 kilometers wide. This view of the Emi Koussi caldera is detailed to the point that it doesn’t include the entire 10-kilometer diameter of the caldera, but reveals individual lava strata within the walls of the summit cliffs. Nested within the main caldera is a smaller crater that contains white salts of a dry lake at its lowest point. Here too, strata are visible in the walls of the smaller crater. The smaller crater is surrounded by a region of darker rocks—a geologically young dome of lava studded with several small circular volcanic vents.