Ol Doinyo Lengai is a unique and extremely fascinating volcano that is located in the African Rift valley about 120 km NW of Arusha, Tanzania.  It is the only volcano in the world that erupts natrocarbonatite lava, a highly fluid lava that usually 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 small flows known as "squeeze-ups" that are light gray when they flow and solidify.  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 brown powder. In 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.

Since the late 1980's, activity at Ol Doinyo Lengai has been witnessed by many observers.  The activity is usually centered in one or more of the small cones that have been formed on the crater floor by previous eruptions of lava. Eruptions have typically taken the form of open lava pools or lakes that may or may not be overflowing, lava flows issuing from holes or cracks inside or near the base of the cones, or lava splashes or fountains from the summit vents of the cones.  The activity is not well understood but is thought to be a function of the plumbing of the crater, the level of the lava within the plumbing, and the gas content of the lava.  No one knows what causes the lava to flow out at any particular time or how the various vents in the crater are interconnected.  Mineralogists would like to understand how the lava evolves under the surface and why it has its unusual chemical composition, but that also is unknown.  Finally, no one has any idea when the present pattern of frequent small lava flows will give way to explosive activity like that seen in 1966 and to a lesser extent in 1993.


I have climbed about 50 active volcanoes in various parts of the world, but Ol Doinyo Lengai has captured my interest like no other volcano ever has.  As of 2006 I have climbed Ol Doinyo Lengai 11 times and have spent 104 nights camping at the summit craters.  During my first visit on July 17, 1997, I went up and down in one day and spent about 4 hours in the crater.  There was some very minor activity, but four hours is not long enough to have a very good chance of seeing an eruption.  I decided that I wanted to spend several nights there to increase my chances of seeing some flowing lava, which is what I did twice in 1998 and once in 1999.  The more time I spent on Ol Doinyo Lengai, the more fascinated I became. In July 2000 and July 2001 I organized camping expeditions to the crater for small groups of clients.  In August 2002 my expedition, which included photographers, a film team, and a volcanologist, encountered hazardous camping conditions due to violent lava fountains and extremely rapid lava flows.  Part of our camp was destroyed by lava and a Tanzanian guide was injured.

In 2004, after my expedition group of 8 people camped for a week at the summit craters, I remained there for another 23 nights to gather data for a research project being conducted by Josh Gordon, a student in the Middle Tennessee State University Geociences Department in Murfreesboro, Tennessee.   In 2005 I returned to Lengai with Josh and three others for a three-week stay at the craters.  Activity was unusually low compared to all of my previous visits, and we obtained much less data than we had hoped to collect.  After a very strong lava eruption in March-April 2006, my four-night Aug 2006 visit, during a period of no activity, allowed close inspection of a large collapse zone that has formed in the central crater.