The surface is the relatively thin covering of soil and unconsolidated rock waste. 浮土是由土壤和未固结岩屑组成的比较薄的覆盖层。
A thick, overlying layer of seafloor rock and sediment would also serve as an additional natural seal to prevent escape. 由海底岩石和沉淀物组成的稠密覆盖层同样会作为一道额外的天然封条防止泄漏。