SAN JUAN, Puerto Rico—Volcanoes that have been quiet for decades are rumbling to life in the eastern Caribbean, prompting officials to issue alerts in Martinique and St. Vincent and the Grenadines as scientists rush into study activity they say hasn’t been observed in years. The most recent warning was issued late Tuesday for La Soufriere volcano in St. Vincent and the Grenadines, a chain of islands home to more than 100,000 people. Officials reported tremors, strong gas emissions, formation of a new volcanic dome, and changes to its crater lake. The Caribbean Disaster Emergency Management Agency said that scientists observed an “effusive eruption within the crater, with visible gas and steam” on Tuesday. The government warned those living near the volcano to prepare to evacuate if needed, declaring an orange alert that means eruptions could occur with less than 24 hours’ notice. La Soufriere, located near the northern tip of …