The surface of the upper slopes of Mauna Loa is almost wholly of two widely different kinds of barren lava-flows, called by the Hawaiians the pahoehoe and the aa.
The principal rivers of this region are Sama (which forms the provisional boundary line with Peru), Tacna, Camarones, Loa, Copiapo, Huasco, Elqui, Limari and Choapa.
The Loa is the largest, having its sources on the slopes of the Cordillera south of the Minho volcano, between 21° and 21° 30' S.
Mauna Loa (" Great Mountain "), on the S., is by far the largest volcano in the world; from a base measuring at sea-level about 75 m.
Of Mauna Loa, and blending with it in an intervening plateau, is Mauna Kea (" White Mountain," so named from the snow on its summit), with a much smaller base but with steeper slopes and a crowning cinder cone 13,823 ft.