根据下面内容，回答题： A group of scientists rowing toward the center of a lake saw something shocking. They turned back as fast as they could. What had they seen? The lake was boiling! The group was investigating a crater lake in the mountains of St. Vincent. A crater lake is the mouth of a volcano that has been dormant for some time and has filled with water. This particular crater was the tip of a volcano called Soufriere， which erupted last in 1902. Since that time， it had not shown any signs of action. But in the fall of 1971， mountain climbers who had hiked near the lake returned to the lowlands with strange stories. They said the water had turned yellow and was giving off a smell like burnt eggs. A seething fog was rising from the lake's surface. Local scientists rushed to Soufriere to see if this might be the beginning of a new volcanic explosion. They found a huge black mass in the middle of the water. It was a great blob 1，000 feet long and 300 feet wide. Lava had pushed up through the bottom of the lake and formed a new island. The investigators wanted to make sure that the volcano was safe， and that the lava would not overflow into the surrounding countryside， But they could never reach the island to study it， because the lava was so hot that the water around it bubbled and boiled. This passage is about________. 查看材料