Overview
This lecture covers the three main explosive eruption landforms—composite volcanoes, cinder cones, and calderas—highlighting their characteristics, formation processes, and notable examples.
Composite Volcanoes (Stratovolcanoes)
- Composite volcanoes (stratovolcanoes) are cone-shaped mountains built from multiple layers of lava and ash.
- They are commonly found in subduction zones, such as the Ring of Fire.
- Examples include Mount Rainier and Mount St. Helens in the U.S., and Mount Fuji in Japan.
- The Cascade Range houses many composite volcanoes due to the Cascadia subduction zone.
- These volcanoes are capable of highly explosive eruptions, frequently altering their shape and size.
- Eruptions can occur repeatedly over thousands of years, as with Mount St. Helens.
Cinder Cone Volcanoes
- Cinder cones are small, steep-sided, conical volcanoes made from loose pyroclastic fragments like cinders and ash.
- Eruptions produce gravel-sized cinders, which are sharp and hazardous.
- They can form on the sides of larger volcanoes (parasitic cones) or as standalone features.
- Notable examples include Paricutin in Mexico and cinder cones near Mauna Loa in Hawaii and in Arizona and Utah.
- Cinder cones are smaller and less durable than composite volcanoes, built from loose materials.
Calderas
- Calderas form when a composite volcano’s magma chamber empties during a large eruption, causing the summit to collapse.
- The resulting depression may refill with magma, beginning the volcanic cycle anew.
- Crater Lake, Oregon, is a caldera formed by the explosion of Mount Mazama approximately 7,700 years ago.
- Yellowstone National Park sits within a massive caldera formed by past explosive eruptions.
Key Terms & Definitions
- Composite volcano (stratovolcano) — Cone-shaped volcano made of layered lava and ash, common in subduction zones.
- Cinder cone — Small, steep volcano built from loose pyroclastic fragments (cinders, ash).
- Caldera — Large depression formed by the collapse of a volcano after a major eruption empties the magma chamber.
- Pyroclastic material — Fragmented volcanic debris, including ash and cinders.
- Subduction zone — Area where one tectonic plate sinks beneath another, often generating explosive volcanoes.
Action Items / Next Steps
- Review the eruption case studies of Mount St. Helens and Yellowstone later in the module.
- Prepare to study effusive eruption landforms in the next lecture video.