Climbing an active volcano, even one seemingly at rest, has hazards that are unfamiliar to most hikers. For these, it is not enough to have plenty of water, stout shoes, adequate clothing, and a flashlight.

The following hazards and associated injury are listed in their probability of occurrence during relatively quiet times at Oldoinyo Lengai.

Serious falls on unstable ground
Near-vent areas are frequently a terrain of ground cracks, rotten spongy rock, and steep crater throats. Avoid perilous slopes and areas marked by freshly broken ground. The fact that Oldoinyo Lengai’s crater-filling lava may be a solid deck one day and a threatening hole the next is testimony to the instability of the summit area. Err on the side of caution. Even a sprained ankle is a serious injury atop a volcano. Broken bones put an entire climbing group at risk of exposure.

Burns, burns, burns
The stories of serious burns from lava flows and degassing fissures are true. Newly emplaced lava, even if dark in appearance, still holds heat far above the boiling point of water. What looks like a solid lava-flow surface may in fact be only a fragile shell, and a person’s weight is sufficient to break through, exposing feet and legs to searing heat.   In 2007, a near fatal accident in poor visibility left one Maasai porter maimed for life.

Noxious gas, the silent killer
Carbon dioxide (CO2) is the second-most abundant gas that issues from Oldoinyo Lengai. (As at all volcanoes, water is the most abundant.) Odorless, invisible, and heavier than air, CO2 accumulates in low-lying areas, where it may reach toxic concentrations. Asphyxiation occurs without warning. Fortunately, winds disperse the gas safely across most of the summit’s active crater. Climbers should avoid deep or steep-sided pits, fissures, and other topographically closed depressions. These poorly ventilated areas may have toxic gas concentrations. Don’t camp at the summit. Those on scientific expeditions that require an overnight stay should rest in the inactive south crater.

Lava flows downhill, fills gullies
Lava flows spill sporadically from the summit crater or escape from fissures high on the volcano’s flanks and flow quickly down its steep slopes. Like any liquid, molten lava favors gullies and ravines, so ridgelines are the safest place to minimize risk. Carbonatite lava which characterizes many eruptions at Oldoinyo Lengai during the past 50 years, is more hazardous than other kinds of lava because it flows so readily (has low viscosity).

Summit explosions are deadly, so stay clear
Stay off the volcano when it is in a period of explosive activity. Explosions are intermittent and unpredictable during such periods. No one could have survived the large summit explosions of 2007 and 2008. Even the luckiest, who might have survived their injuries from the large volcanic bombs in the fallout, would have died when choked by the abundant near-vent ash. At such times, an added hazard exists for pyroclastic flows and surges. These are the “glowing clouds” that spill down a volcano’s flanks at hurricane velocity whenever upward-thrusting, dense ash plumes become gravitationally unstable and collapse back onto the summit area.

Many thanks to David Sherrod, Cascades Volcano Observatory, USGS for expert advice.

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