*****UPDATE 9/22*****The smoke coming from Meru volcano was indeed a forest fire and NOT a volcanic eruption. While it is unclear whether reports of tremors are accurate, it is confirmed that no eruption has taken place.
Sep 20, 2015 -Tanzania
Meru volcano, which has not erupted in a hundred years or so, may have had an eruption. Reports are coming in from several sources, although all of them are posting the same image. The image appears to show the NE flank of the volcano in eruption, however it is too soon to tell and 'could' be a wildfire. The image does appear however to show large amounts of grey ash, and being a California native, I can tell you most brush fires burn very much darker than that, so it does look like it could be volcanic.
Image by Selle Higgins (@safariwithselle Twitter) via VolcanoDiscovery.com
The surrounding areas are mostly farmlands with some small villages, so not a very high population center, however any large pyroclastic flows could have devastating consequences for those on its slopes. If the picture (which is a bit hazy) is interpreted correctly, the eruptive center appears to be on the lowe flank of 'Little Meru', a satellitic summit cone/dome to the NE of the main summit (similar to Mt. Shasta's 'Shastina' cone. The blast could be lateral, or there may be a small amount of pyroclastic flow that is travelling down the flank, far too soon to know.
The Smithsonian GVP characterizes Meru:
"Meru volcano, Africa's fourth highest mountain, is dwarfed by neighboring Kilimanjaro volcano, but is an impressive peak in its own right. Seen from the west, Meru has a conical profile, but it contains a 5-km-wide breached caldera on the east side that formed about 7800 years ago when the summit of the volcano collapsed. Associated massive debris avalanches and lahars traveled as far as the western flank of Kilimanjaro volcano. Parasitic cones and lava domes are located on all sides; a maar field is present on the lower north flank. The historically active Ash Cone forms a prominent symmetrical cone inside the breached caldera. A second vent between it and the caldera headwall has fed lava flows that cover much of the caldera floor."
At this time however, this could be a false alarm, as there are doubts this is actually a volcanic eruption, and rather could simply be a wildfire. This video seems to suggest it is just a wildfire: