Shala, Ethiopia

Location: 7.47N, 38.55E
Elevation: 6,806 ft.(2,075 m)
Lake Shala is the deepest lake (257m) and the largest crater (~12x15 km) in Ethiopia. Volcanologically, the Shala basin is a caldera which probably collapsed during the late Pliocene (about 3-4 mya) following large eruptions of ignimbrites and pumice. The relations between the pre-existing volcanic rock of the rift valley and Shala's products are unclear, but it is likely that the ignimbrites around Langano, Zuway, and other places in the rift came from Shala. Thick, light colored pumice units exposed high on the south rim of the caldera undoubtedly are from the Shala eruption. Erosionally isolated stacks of ignimbrite and pumice occur on the north rim of the caldera near the track to Abiata.

Hotsprings along shoreline of Lake Shala.

Aerial photographs show many strand lines, representing previous temporary high lake levels, on Shala's southern shore. Between about 10,000 and 5,000 years ago a large part of the rift valley was covered by a large lake, now called the Galla Lake, which was about 110m above the present level of Lake Shala. Shala was then marked only by circular string of disconnected islands, the tops of the highest peaks of the rim.

Chitu Crater

Probably sometime during this high lake period - or a previous one - eruptions of basaltic lava through the lake produced the tuff ring now occupied by Lake Chitu, about 1.5 km south of Shala. In Gallinya, 'Chita' means 'that which is broken or separated' refering to a local tradition that Chitu was once connected with Shala, but the tow lakes separated long ago as the level of Shala declined. Strand lines within Chitu prove that its water level was once higher, but it seems improbable that the Galla, who only entered this part of Ethiopia within 400-500 years, could have ethnic memories of the high lake levels from 5,000 years ago. Were there more recent high lake levels in Chitu, or connecting Chitu with Shala?

Lake Chitu with a flock of flamingos along its shoreline.

Chitu is a beautiful crater lake (crater diameter of 1.6 x 1.2 km) with a population of 5,000-10,000 flamingos. The crater's rim (about 80 m above lake level) is composed of gray tuff containing bomb sags, cross-bedding and dune/antidune structures, comfirming that it erupted through a shallow lake. Whitish, inward dipping sediments occur up to 30 m above the lake. About 2 km south of Chitu an arcuate ridge is all that remains of two other tuff rings (one about 1.4 km and the other about 0.8km in diameter), somewhat older than Chitu. This ridge is called Maja Faro, meaning "Water was once there"; and the local Galla people say that Lake Shala extended into this eroded ring-pair only three generations earlier. It is impossible for Shala to have been that high so recently; but perhaps if the rainfall were only slighly higher then, a shallow swampy lake could have existed during rainy seasons.

Two other highly eroded tuff rings are loacted north of Chitu on the shore of Shala, indicating that all of the rings - and the small amounts of basalt - were erupted through north, northeast fractures along the Wonji Fault Belt. These rings contain numerous bomb sags and accretionary lapilli (indications that tuffs were wet at the time of deposition), and large parts of their rings have been destroyed by Shala wave action. Other arcuate sections along the Shala rim may be tuff rings, but they have not been investigated on the ground. A large, nearly complete 4 km wide embayment on the south-east rim of Shala may be a tuff ring or it may be a small caldera.

Small collapses a few meters across occur along approximate North-South lines between Shala and Chitu. One imprssive, vertical walled hole is about 10 m deep and seems to have a horizontal opening at the bottom. These collapses have probably formed within sediments filling a tentional fissure - a gya - such as occur near Negheli and Fantale.

This interesting, beautiful and largely unexplored southern shore of Shala can be reached by driving 23 km along the Shashamane-Soddu road and then following a four wheel drive track a futher 25km north to the lake.

Sources of Information: Charles A. Wood. (PI VolcanoWorld)

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