ALMA telescopes with the backdrop of volcanoes on Chile Altiplano. ALMA (Atacama Large Millimetre/sub-millimetre Array) is an array of 66 radio antennas located at an elevation of 5000 m on the arid Chajnantor plateau in the Chilean Andes. Data from the separate antennas is combined by interferometry, making it one of the most powerful telescopes in the world.