( CNN ) -- An ice jam on the Yukon River in Alaska sparked flooding in the city of Galena , where some 300 people have been evacuated , authorities said . Most of the people who left their homes were being housed in either Ruby or Fairbanks , said Kerry Seifert , operations section chief at the Alaska Division of Homeland Security and Emergency Management . Some are at shelters , while others were with friends and relatives . `` We expect the flooding to become worse before the waters start to recede , '' said Alaska Gov . Sean Parnell , who surveyed the damage this week . `` Ensuring the safety of those impacted by the flooding remains my top priority . '' According to Seifert , the cause of the jam was a late break up of ice . Colder temperatures meant there was no melting until a rapid warming put lots of water in the river basin . A wall of ice got hung up at a steep curve in the river near Galena , he said . Water appeared to be beginning to move around the sides of the ice Wednesday , Seifert said , which could be good news for people living in Galena . When the jam breaks , however , downriver communities of Koyukuk and Nulato may be at risk . Alaska volcano `` fountains '' with fire , spreads expansive ash cloud .
A wall of ice got hung up at a steep curve in the Yukon River . Some 300 people are evacuated . `` We expect the flooding to become worse before the waters start to recede , '' governor says .