SAN JUAN, Puerto Rico—An explosive eruption rocked La Soufriere volcano on the eastern Caribbean island of St. Vincent on Friday following mandatory evacuation orders from the local government. Emergency management officials said the ash column rose about 20,000 feet high and that the ash was headed east into the Atlantic Ocean. However, heavy ashfall also was reported in communities around the volcano, said Erouscilla Joseph, director of the University of the West Indies Seismic Center. “More explosions could occur,” she said in a phone interview, adding that it was impossible to predict whether they might be bigger or smaller than the first one. There were no immediate reports of casualties. In the coastal town of Barrouallie, about 9 miles from the volcano, evacuees trudged toward shelters carrying backpacks, duffel bags, and shopping bags stuffed with personal belongings after the explosion. Some prepared to stay there, while others were expected to …