Geologists climbed to the summit . . . on 10-11 November, for the first time in many years. Members of the group made the first known descent into the active S crater . . . (figure 4). The active pit-crater was >100 m in diameter, with vertical walls and a lava lake at 100 m depth (figure 5). A winch and ropes were used to descend the E wall on the morning of 11 November for a 2-hour visit. The 40 x 70 m lava lake occupied the W part of the crater. Air temperature at the bottom of the crater was 35°C, ~5°C cooler than the ambient temperature at the rim. Wearing gas masks, geologists approached to within 2 m of the lava lake. The lake was continuously active with 4-5-m-high lava fountains in four locations and rapid motion of the lake surface outward from the center. The N crater was confirmed to be inactive, with the bottom full of fallen rock, although there were two strong fumaroles on the S rim.

Figure 4. Summit caldera of Erta Ale, April 1972, showing the N and S craters. Lava spillways over the caldera rim are shown diagrammatically. Sketch by Jacques Varet.

Figure 5. Diagrammatic plan view (top) and cross-section (bottom) of the active S crater at Erta Ale, November 1992. Courtesy of P. Vetsch.

Geological Summary. The Erta Ale basaltic shield volcano is the most active in Ethiopia, with a 50-km-wide edifice that rises more than 600 m from below sea level in the barren Danakil depression. It is the namesake and most prominent feature of the Erta Ale Range. The volcano includes a 0.7 x 1.6 km elliptical summit crater hosting steep-sided pit craters. Another larger 1.8 x 3.1 km wide depression elongated parallel to the trend of the Erta Ale range is located SE of the summit and is bounded by curvilinear fault scarps on the SE side. Fresh-looking basaltic lava flows from these fissures have poured into the caldera and locally overflowed its rim. The summit caldera usually also holds at least one long-term lava lake that has been active since at least 1967, or possibly since 1906. Recent fissure eruptions have occurred on the N flank.

Information Contacts: P. Vetsch, M. Vigny, and A. Schussele, SVG, Switzerland; L. Cantamessa, Géo-découverte, Switzerland; G. Pareau, Assoc of Alpine Guides of Chamonix, France; P. Villemin and A. Curvelier, Gaumont Television, Paris, France.