Grimsvotn volcano eruption spews steam, ash and smoke in central Iceland, May 23, 2011. /CFP
Iceland on Thursday said it was closely monitoring its most active volcano after its glacier lake burst, an event that could trigger an eruption.
The Grimsvotn volcano, which is located in an uninhabited and remote area of central Iceland, is situated under the Vatnajokull glacier, which is the largest in Europe.
Authorities have raised the alert level for the Grimsvotn to "yellow," a color code that is used to warn the aviation industry of the risk of eruption.
A red alert means an eruption is considered imminent.
The Icelandic Meteorological Office (IMO) said on its website that a tumultuous glacial flow had formed near the volcano.
After the Grimsvotn volcano erupted and spew ash, farmers wear masks and gather their sheep in Borgarnes, western Iceland, May 23, 2011. /CFP
Grimsvotn's most recent eruption in 2011 sent plumes of ash into the atmosphere that caused relatively minor air traffic disruptions, when around 900 flights were cancelled.
A glacial flow caused other eruptions in 1922, 1934 and 2004.
Grimsvotn's seismic activity in recent months has been higher than normal, the IMO said in a statement.
The last volcanic eruption in Iceland, less than a month ago just south of the capital Reykjavik, saw the small town of Grindavik, home to 4,000 inhabitants, evacuated as a precautionary measure.
Iceland has seen four volcanic eruptions in the last two years.