Both oil and gas are less dense than water, so they generally tend to rise upward through water-saturated rock and sediment.
石油和天然气的密度都比水小，所以二者通常会浮在被水浸泡的岩石和沉积物的表层。
2
The eruption seems to have started with the volcano spitting out lumps of rock up to 2 metres across, before releasing an enormous pyroclastic flow - a fast-moving gush of hot gas and rock.