REYKJAVIK, Iceland — A volcano in southern Iceland has erupted for the first time in almost 200 years, raising concerns that it could trigger a larger and potentially more dangerous eruption at a volatile volcano nearby.

The eruption at the Eyjafjallajokull volcano, located near a glacier of the same name, shot ash and molten lava into the air but scientists called it mostly peaceful.

It occurred just before midnight Saturday at a fissure on a slope — rather than at the volcano’s summit — so scientists said there was no imminent danger that the glacier would melt and flood the area.

TV footage showed lava flowing along the fissure, and many flights were canceled due to the threat of airborne volcanic ash. After an aerial survey Sunday, scientists concluded the eruption struck near the glacier in an area that had no ice.

“This is the best possible place for an eruption,” said Tumi Gudmundsson, a geologist at the University of Iceland.

Nonetheless, officials sent phone messages to 450 people between the farming village of Hvolsvollur and the fishing village of Vik, urging them to evacuate immediately.

A state of emergency was declared although there were no immediate reports of injuries or damage. Evacuation centers were set up near the town of Hella, but many people returned to their homes later Sunday. The most immediate threat was to livestock because of the caustic gases the eruption released.

“We had to leave all our animals behind,” farmer Eli Ragnarsdottir said at an evacuation center. “We got a call and a text message … and we just went.”

Scientists say it is difficult to predict what comes next.

“It could stop tomorrow, it could last for weeks or months. We cannot say at this stage,” Gudmundsson said.

The last time there was an eruption near the 100-square-mile Eyjafjallajokull glacier was in 1821, and that went on slowly and continuously for two years.

The latest eruption came after thousands of small earthquakes rocked the area in the past month. Scientists in Iceland have been monitoring the volcano using seismometers and global positioning instruments, but Gudmundsson noted that the beginning of Saturday’s eruption was so indistinct that it initially went undetected by the instruments.

“The volcano has been inflating since the beginning of the year, both rising and swelling,” said Pall Einarsson, a geophysicist at the University of Iceland’s Institute of Earth Science.

“Even though we were seeing increased seismic activity, it could have been months or years before we saw an eruption like this … we couldn’t say that there was an imminent risk for the area.”

However, Einarsson and Gudmundsson said the eruption could trigger a more damaging eruption at the nearby Karla volcano, which lies under the thick Myrdalsjokull icecap and threatens massive flooding and explosive blasts if it erupts.

First settled by Vikings in the 9th century, Iceland is known as the land of fire and ice because of its volcanos and glaciers. During the Middle Ages, Icelanders called the Hekla volcano, the country’s most active, the “Gateway to Hell,” believing that souls were dragged below.