A second feature of maritime Southeast Asia is the seas themselves. Apart from a few deep underwater trenches, the oceans are shallow, which means they are rather warm and not very saline. This is an ideal environment for fish, coral, seaweeds, and other products. Though the seas in some areas are rough, the region as a whole, except for the Philippines, is generally free of hurricanes and typhoons. However, there are many active volcanoes and the island world is very vulnerable to earthquake activity.