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On 21 May 2011, Grimsvoetn volcano rumbled to life and sent off a plume of ash and steam about 20 km (12 mi) into the atmosphere. Above Grimsvoetn's summit, volcanic ash formed a circular brown plume that towered above the surrounding clouds. In the southeast, ash colored the snow surface dark brown. Ash from the volcano also reduced visibility to about 50 m (160 ft) in some areas, causing night-like darkness in the middle of the day. Image courtesy of NASA.