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.
Above Grímsvötn’s summit, volcanic ash forms a roughly circular 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, the Eruptions blog stated. Iceland Review Online reported that ash falling from the volcano caused some areas turn as dark as night in the middle of the day. The ash plume also prompted the closure of Keflavik, Iceland’s largest airport.
The initial plume from Grímsvötn was higher than that from Eyjafjallajökull, which only reached 8 kilometers (5 miles). Despite its taller plume, Grímsvötn was expected to hamper trans-Atlantic air traffic less than Eyjafjallajökull had, at least in the first 24 hours. Grímsvötn’s ash was forecast to travel toward the northeast, the Icelandic Met Office stated. In addition, the ash content was coarser and therefore less likely to remain airborne long enough to reach European airspace. Some volcanic ash models, however, suggested that Grímsvötn’s ash could interfere with flights in the United Kingdom and Ireland beginning on May 24.
Volcanic plumes can produce lightning, and the plume from Grímsvötn produced an intense lightning storm. At its peak, the lightning storm from this volcano produced 1,000 times as many lightning strikes per hour as Eyjafjallajökull had over a year earlier.
Much of Grímsvötn lies below the Vatnajökull Glacier. Consequently, when the volcano first started erupting in May 2011, the eruption was subglacial. Such eruptions can cause glacier outburst floods, or jökulhlaups. The Icelandic Met Office stated, however, that because an outburst flood had already occurred the previous autumn, a big flood appeared unlikely in the spring of 2011.