REYKJAVIK, Iceland — A volcano under a glacier in Iceland erupted Wednesday for the second time in less than a month, melting ice, spewing smoke and steam, closing a major road and forcing hundreds of people to flee rising floodwaters.

Authorities evacuated 800 residents from around the Eyjafjallajokull glacier as water gushed down the mountainside and rivers rose by up to 10 feet

Iceland’s main coastal ring road was closed near the volcano.

Workers smashed holes in the highway in three spots in a bid to give the rushing water a clear route to the coast and prevent bridges from being swept away.

Vidir Reynisson, a manager with Iceland’s Civil Protection Department, said that by late afternoon the flooding appeared to have peaked.

“But the water is still flowing down to the ocean,” Reynisson said, “so it will be some hours before we have a better view of what kind of damage has occurred.”