Activity: 1998, Lava Overflow

On 1 November 1998 Burra Ami Gadiye’s photograph taken looking westwards along the north wall (photograph to left, below) showed that by then lava had begun to overflow the low point on the crater rim. Burra’s caption for this photograph says (in Swahili) “jinsi crater ilivyojaa na kumwaga lava upande wa rimu ya kzmg” – “how the crater has filled up and is pouring lava on the side of the northwest rim”. On 20 November 1998 Benoit Wangermez flew over the summit crater and his photograph (to right, below) shows several narrow young dark flows on the central crater floor and (probably) small amounts of lava overflowing both the northwest rim (in the foreground) and the east rim (in the background).

Burra Gadiye’s photograph (left below) was taken on 19th November 1998 and shows him on the east rim, touching the cool somewhat weathered lava that had flowed over the rim a few weeks earlier. His caption on this photograph is “Nikiwa kwenye rimu ya ms jinsi ilivyojaa na kumwagika na kuunguza majani yote ya upande wa ms” “When I was on the east rim showing how it is full and spilling out and has burnt all the grass on the east side”. Activity continued later that month, as shown by Burra’s photograph from 24 November 1998 (right below) and continued throughout the first half of 1999.

Franck Pothe and a group from Terra Incognita observed spectacular sprays of lava and activity in two lava lakes between 8 and 10 March 1999; see the two photographs below.

Over the following months, lava continued to flow over the northwest rim, as shown in Eric Christin’s photograph below, taken in early 1999.

During early 1999, as well as flowing over the east rim, lava burst out of small vents high on the outer east wall of the cone, as shown in photographs by Francois Martel (left below) and Eric Christin (right below).

In early March 1999 Franck Pothe observed lava flowing down the east wall; see photograph on left below. By late July 1999 the lava flow down the east wall had reached over half way down the outer slope. The photograph to the right below, taken by Celia Nyamweru on 26 July 1999, shows narrow white tongues of lava extending from the crater rim, to the left (south) of the bare ash slopes dating from 1966 and 1967.

The view on the east crater rim in late July is shown in the left hand photograph below. The width of the overflow at the former rim was about 22 metres. The thickness of the lava at and below the overflow varied. In places it was very thin; dead plants and roots were sticking up through the lava. In other places close by the lava was much thicker; and had formed lava tunnels about 1 to 1.5 metres deep. The youngest lava on the eastern overflow was white at the end of July (see the right hand photograph below) and this suggests that it had been extruded several weeks before these photographs were taken.

The lava had also flowed over the northwest rim; see Celia Nyamweru’s photographs below. The total width of this overflow in late July was about 67 metres,  including a small ‘island’ of the old rim surrounded by younger lava. One overflow (see the left hand photograph) was a small flow, about 5 metres wide as it crossed the crater rim and extending about 5 to 10 metres below the rim. The lower limits of the larger flows (see right hand photograph) could not be seen from the rim, or from looking at the northwest slope from below, but I estimate these flows probably extended at least 150 metres below the rim. Variations in lava colour and texture indicated several different episodes of flow over the northwest rim, the most recent probably a few weeks before the end of July 1999.

What happened next?

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