Leaving Jaggar Museum and continuing around to the left on Crater Rim Drive, the road winds its way toward the floor of the caldera and Halema`uma`u crater. Along the way, you will stop at the sign for the Southwest Rift Zone.
Note: This area is directly downwind from Halema'uma'u Crater and if anyone in your group has breathing or heart problems, or is pregnant, or if your group includes infants or young children -- bypass this stop. Roll up your car windows and continue driving until you reach the Keanakako'i Overlook, stop #6 on this tour.
As you approach Halema'uma'u Crater from Jaggar Museum, Crater Rim Drive crosses Kilauea's southwest rift zone, here visible as deep fissures, fractures and gullies. Rift zones are regions of weakness along a volcano's flanks and are areas where eruptions are likely to happen. The southwest rift zone starts at Kilauea's summit and continues to the seacoast and beyond. Some of the large cracks that you see along the roadway were formed after the large earthquake of 1868. The strata in the walls of the fissure are ash, cinder, and pumice from the 1790 eruption.
Notice, also, the lack of vegetation. This area is showered with naturally occurring acid rain. The Halema'uma'u Crater spews forth about 300 tons of sulfur dioxide daily. This is oxidized in the air and when moisture is present the sulfur dioxide returns as sulfuric acid. This area receives 30 to 40 inches of rain per year, an amount that would support a diverse ecosystem were it not for the effects of acid rain.
