Ol Doinyo Lengai

volcano, altitude 2886 meters (9524 feet), is a unique and extremely fascinating volcano that towers above the East African Rift Valley in Northern Tanzania, just south of Lake Natron. It is the only volcano in the world that sometimes erupts natrocarbonatite lava, a highly fluid lava that contains almost no silicon. Natrocarbonatite lava is also much cooler than other lavas, being only about 950 degrees F (510 degrees C) compared to temperatures over 2000 degrees F (~1100 degrees C) for basaltic lavas. Natrocarbonatite is the most fluid lava in the world. Lava with a low gas content can flow like a whitewater stream, and actually has a viscosity near that of water. Natrocarbonatite lava glows orange at night, but is not nearly as bright as silicon-based lavas since it is not as hot.

During the day it is not incandescent; most flows look like very fluid black oil, or brown foam, depending on the gas content. In the past, some visitors to the crater believed they were seeing mud flows. Most newly solidified lava is black and contains crystals that sparkle brightly in the sun. There are also sometimes small flows known as “squeeze-ups” that are light gray when they flow and harden. Contact with moisture rapidly turns natrocarbonatite lava white because of chemical reactions that occur when the lava absorbs water. Eventually the water absorption process turns lava flows into soft brown powder.

During dry weather the whitening of flows happens over a period of a few days to a couple of weeks, depending on the thickness of the flow. In rainy weather the lava surface turns white immediately. In parts of the crater that have been inactive for several months, the ground is light brown/white and so soft that one sinks into it when walking.