So, there were about ten volcanic eruptions...

...in Iceland from June 1783 through February 1784. The Nile River had record low water levels in 1783-84, after the Laki eruptions. There was also low Nile River flow in 939 A.D., following the Eldgjá eruption in Iceland. In 1912, the Niger River had a record low level after the Mount Katmai, Alaska, eruption. Volcanic eruptions in high latitudes have happened right before weakened African and Indian monsoons and slow tree growth in Alaska and Siberia. Etc., etc., etc. See Historic Volcanic Eruption Shrunk the Mighty Nile River, November 21, 2006, at NASA's website for the story.

See also CALIPSO's First Images Offer New Dimension to Air Quality and Climate Research, July 24, 2006, for info on one of NASA's newest satellite missions, which amongst other things can detect and track volcanic plumes in the atmosphere. CALIPSO, if you were wondering, is the easy way of saying Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations.

I didn't know what lidar meant, but the article explains:

CALIPSO's innovative lidar system is an active remote sensing technique, similar to radar in operation. The lidar emits short pulses of green and infrared light -- rather than the microwaves used by radar -- which are reflected from cloud and aerosol particles in the atmosphere. Each lidar sample produces a 300-feet wide snapshot or profile of the atmosphere. Profiles collected along an orbit are streamed together to paint a picture of what a vertical slice of our atmosphere looks like.

No, I don't know how to pronounce lidar. I'm still looking for that bit of info. (Or, more precisely, I will look when I have more time.)

"CALIPSO is a joint U.S. (NASA) and French (Centre National d'Etudes Spatiales/CNES) satellite mission with an expected 3 year lifetime," according to this NASA website.