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.
The theory of plate tectonics holds that the Earth's geological processes, from earthquakes and volcanoes to mountain-building and continent formation, are the result of the slow movements of a dozen or so gigantic slabs that shift over the asthenosphere, a molten region of the upper mantle.