a branch of the Indo-European family of languages, including especially Irish, Scottish Gaelic, Welsh, and Breton, which survive now in Ireland, the Scottish Highlands, Wales, and Brittany. adjective. 2. of the Celts or their languages.
Movement of tectonic plates-higher. Volcanoes, mountains and earthquakes occur at the edges of tectonic plates-their creation depends on the direction the plates are moving.
Together, the crust and upper portion of the mantle â called the lithosphere â are where most important geological processes occur, such as mountain-building, earthquakes and the source of volcanoes. The slow churning and overturning of the mantle is what drives the movements of Earth's tectonic plates.