The height of Etna is so great that its slopes can be divided into three distinct climatic zones or belts. The lowest of these lies between the sea and a height of 2,500 feet. In this zone the mountain slopes are covered with cultivated fields, olive groves, orchards, and vineyards. The middle zone lies between 2,500 feet and 6,270 feet. This zone is covered with forests of chestnuts, oaks, beeches, and cork trees. The third and highest zone includes the rest of the mountain, and may be called the desert zone, since it is a sterile region, covered with huge blocks of lava and scoriæ, and terminating, in the higher portions, in a snow-covered plain, from which the central cone rises.
Etna is continually sending up columns of steam and sulphur vapor. Every now and then it starts in eruption, throwing out large quantities of lava either from the crater on its summit, or from some of the 200 smaller cones or craters that occupy portions of its slopes. On account, probably, of its height the eruptions are most frequently on the sides. Etna affords a magnificent example of a huge volcanic pile of the Vesuvian type, which has been slowly built up by the gradual accumulation of materials that have escaped from its craters.
One of the most interesting features of the higher regions of Etna is an immense chasm rent in a side of the cone near the summit, and known as the Val del Bove. This chasm forms a vast amphitheater.
The great force that removed such an immense mass of matter from the cone could not have been the eroding power of water, since the materials of the cone are too porous to permit streams of any size to rush down the slopes. The force is most probably to be found in some explosive eruption of the mountain, when a portion of the crater was suddenly blown off, just as was done in Vesuvius when a large part of the old crater of Somma was blown away. What is especially interesting about the Val del Bove is the opportunity it affords for studying the interior structure of the mountain, for it practically enables one to enter to almost the heart of this great volcano.
The Val del Bove has the shape of a great pit five miles in diameter. It has almost vertical walls, the height of which varies with their position. Those which reach highest up the mountain vary from 3,000 to 4,000 feet in height.