Since the melting of the last ice-cap over Shetland approximately 10 000 years ago water has filled the over deepened valleys and depressions carved out by the ice to leave a flooded landscape of islands and inlets (voes). New landforms such as sand spits, ayres and tombolos have been built up as the sea has reworked sediments of sand, gravel, pebbles and shingle. Shetland is the only part of Scotland where there is no known evidence of sea levels higher than present. Throughout mainland Scotland a process known as isostatic uplift is taking place. This means that land that was pressed down under the weight of glacial ice is rebounding upwards now that the ice has melted. The land is currently rising faster than the sea. However, the weight of ice over Shetland was relatively slight which means that isostatic uplift in Shetland is not keeping pace with rising sea levels.