They also depend on the orientation of fronts and zonation. Tectonic risks are linked to the different types of lithospheric plate boundary. The first type concerns oceanic islands, associated with ridges (Iceland, the Azores) and hotspots (Hawaii), where volcanism is effusive in most cases. Active margins subjected to convergent plate dynamics are higher risk areas. Margins where plates collide are, by nature, rarely located near seas, except in the case of the Mediterranean basin, where volcanism is localised, yet active (Etna), and earthquakes are destructive. Subduction margins are areas with high seismic activity and where volcanism is explosive in most cases. The eastern coasts of the Pacific Ocean are concerned by these margins. The intra-oceanic island arcs running from the Bering Sea to New Zealand are even more unstable due to a combination of risks, both tectonic and oceanic (tsunamis). The other marine and coastal risks are associated with oceanic hydrology and the climate, along with their fluctuations, to varying degrees.