The Aeolian archipelago consists of seven islands spread over a 90 km sea arch, along Sicily's north-east coast.They are dispersed in a large Y-shape. Vulcano is at the lower end, with Alicudi and Stromboli respectively being at the west and east extremes. The Aeolian islands are all of volcanic origin; signs of this volcanic activity being the underwater hot water springs and the therapeutic spa mud. The oldest are Alicudi and Filicudi which are approximately 1 million years old. The most recent are Vulcano and Stromboli, which still have volcanic activity. Lipari's islands, thanks to its favourable geographic position, enjoy a typically Mediterranean climate. The average temperatures vary from 10° C in winter, to 20-21° C in spring and autumn, while during the summer the thermometer shows temperatures between 27- 30 C . Rainfall is scarce, especially in summer.