Volcanoes erupted to make the dramatic terrain of Arusha National Park in Tanzania, just east of the huge fault known as the Great Rift Valley. They spewed fire and lava into the air 20 million years ago, then collapsed into two big calderas, the Ngurdoto and Meru craters, which mark the western and eastern boundaries of the 52-square-mile park. Depressions in boiling mud became the Momela Lakes. Today, these lakes are fed by underground streams that leach salt from the alkaline soil and support algae, a few small fish, and thousands of birds, especially grebes and flamingo.

Mount Meru remains a volcano, though dormant since its last conniption in 1910, a lava-streaked peak that rises to 14,979 feet encased by lush forests and bare rock. The fifth highest mountain in Africa, Mt. Meru is favored by climbers who want to avoid the heavier foot traffic on Mt. Kilimanjaro less than 50 miles away.

Each of the three main areas, Ngurdoto Crater, the Momela Lakes, and Mt. Meru, contains plants and animals suited to its particular altitude and geology. Ngurdoto Crater is ringed by montane forests, but swamps cover the crater floor. The forests host a wide range of trees, from common cedars to varieties that are so rare outside of Africa that no popular names exist for them in English. Some of the trees bear fruit like mangoes, olives, dates and figs. Primates rule the branches and, of course, eat the fruit. Olive-colored baboon mothers carry their babies like little jockeys, while mature males perch pensively nearby, wisely watching from poodle-nosed faces circled by full manes.

The ascend is quite steep, the route to the summit passes over streams, through parkland, montane forest, a giant heather zone and moorland. The summit is reached by a narrow, barren ridge, which provides stunning views of the Ash Cone lying several thousand feet below in the crater. Weather permitting, Kilimanjaro can be seen in the West.