Global sea levels are rising due to two main factors: eustatic change caused by melting ice sheets and glaciers which adds water to the oceans, and isostatic change where land masses rise or sink in response to being weighed down by ice. As sea levels rise, coastal landforms emerge like raised beaches and relict cliffs, while others submerge to form drowned river valleys called rias and flooded glacial valleys called fjords. Rising seas are predicted to flood low-lying coastal areas and increase erosion, threatening habitats, settlements, infrastructure and fresh water sources over the coming decades.