One year after Eyjafjallajökull rumbled to life, another Iceland volcano began spewing ash and steam. At approximately 17:30 Universal Time (5:30 p.m. local time) on May 21, 2011, Grímsvötn began to erupt. The volcano sent a plume of ash and steam about 20 kilometers (12 miles) into the atmosphere, the Icelandic Met Office reported. Overnight, the plume height dropped to 15 kilometers (9 miles), but occasionally rose to its initial altitude.
The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite captured this natural-color image at 13:00 UTC (1:00 p.m. local time) on May 22, 2011. (MODIS on NASA’s Aqua satellite captured another image of the volcano about 8 hours earlier.)
Above Grímsvötn’s summit, volcanic ash forms a circular brown plume that towers above the surrounding clouds. In the southeast, ash has colored the snow surface dark brown. Ash from the volcano reduced visibility to about 50 meters (160 feet) in some places. Iceland Review Online reported that ash falls prompted the closure of Keflavik, Iceland’s largest airport, and caused some areas turn as dark as night in the middle of the day.
The initial plume from Grímsvötn was higher than from Eyjafjallajökull, which only reached 8 kilometers (5 miles). Despite its taller plume, Grímsvötn was not expected to hamper trans-Atlantic air traffic as much as Eyjafjallajökull, at least in the first 24 hours. Grímsvötn’s ash was forecast to travel toward the northeast, the Icelandic Met Office stated, and it was coarser and less likely to remain airborne long enough to reach European airspace. Some volcanic ash models, however, suggested ash could interfere with flights in the United Kingdom and Ireland beginning on May 24.
Volcanic plumes can provoke lightning, and the plume from Grímsvötn produced an intense lightning storm. At its peak, the lightning storm produced 1,000 times as many strikes per hour as Eyjafjallajökull had a year earlier.