Stratovolcano on Fotopedia

A stratovolcano, also known as a composite volcano, is a tall, conical volcano built up by many layers (strata) of hardened lava, tephra, pumice, and volcanic ash. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile and periodic, explosive eruptions. The lava that flows from stratovolcanoes typically cools and hardens before spreading far due to high viscosity. The magma forming this lava is often felsic, having high-to-intermediate levels of silica (as in rhyolite, dacite, or andesite), with lesser amounts of less-viscous mafic magma. Extensive felsic lava flows are uncommon, but have travelled as far as 15 km (9.3 mi).

Stratovolcanoes are sometimes called "composite volcanoes" because of their composite layered structure built up from sequential outpourings of eruptive materials. They are among the most common types of volcanoes, in contrast to the less common shield volcanoes. Two famous stratovolcanoes are Krakatoa, best known for its catastrophic eruption in 1883 and Vesuvius, famous for its destruction of the towns Pompeii and Herculaneum in 79 A.D.

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San Francisco Pass

The San Francisco Pass is one of the most important passes of the Andes mountains which connects Argentina and Chile. The highest point of this pass is at 4,748 m (15,577 ft) AMSL.

The pass is located at 26°52′35″S 68°18′05″W / 26.87639°S 68.30139°W / -26.87639; -68.30139 and connects the Argentinian province of Catamarca with the Atacama Region in Chile. In the Argentinian side, route N 60 ascends from Fiambala at 1,505 m (4,938 ft) AMSL in a deep valley formed by 5,000-metre (16,000 ft) mountains. In the last sinuous 20 km (12 mi), the route climbs from about 4,000 m (13,000 ft) in Las grutas to more than 4,700 m (15,400 ft) at the border.

On the Chilean side the route CH-31 connects Copiapo with the Chile-Argentinian border. On the way it passes next to Maricunga's salt flat on the Nevado Tres Cruces National Park and Laguna Verde. The area is surrounded by volcanoes and high peaks as the Cerro Falso Azufre (5,906 m or 19,377 ft), the volcano San Francisco (6,018 m or 19,744 ft), the Incahuasi (6,638 m or 21,778 ft) and highest volcano in the world, Nevado Ojos del Salado (6,879 m or 22,569 ft), among others.