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examBoard: Cambridge
examType: IGCSE
lessonTitle: Volcanic Features
Volcanoes are one of Earth's most dramatic and powerful natural features. They form when magma from the Earth's mantle rises to the surface, creating various landforms depending on the type of eruption, magma composition and local geological conditions.
Key Definitions:
Volcanoes come in different shapes and sizes, each with unique characteristics and formation processes.
Shield volcanoes have gently sloping sides and form from fluid basaltic lava flows. They're the largest volcanoes on Earth.
Example: Mauna Loa in Hawaii rises 9 km from the sea floor and is the world's largest active volcano.
Features: Broad, dome-like shape with gentle slopes (usually less than 10°).
Also called stratovolcanoes, these have steep sides and are made up of alternating layers of lava and ash.
Example: Mount Fuji in Japan and Mount St. Helens in the USA.
Features: Steep sides (30-35°), conical shape and often have a summit crater.
Small, steep-sided volcanoes formed from ejected lava fragments that build up around the vent.
Example: Paricutin in Mexico, which famously grew in a farmer's field in 1943.
Features: Simple cone shape, steep sides (30-40°) and a circular crater at the summit.
Formed when thick, viscous lava piles up near the volcanic vent rather than flowing away.
Example: Lassen Peak in California.
Features: Steep-sided, rounded mounds that form when lava is too thick to flow far from its source.
Volcanoes create distinctive landforms both during and after eruptions. Understanding these features helps geographers analyse volcanic activity and potential hazards.
Bowl-shaped depressions at the summit of a volcano, formed by explosive eruptions or collapse.
Most active volcanoes have a main crater at their summit where eruptions occur.
Large, basin-shaped depressions formed when a volcano collapses into its empty magma chamber after a major eruption.
Calderas are much larger than craters and can be several kilometres wide.
Formed when magma solidifies in a volcano's vent, creating a resistant rock formation that remains after erosion removes surrounding material.
Edinburgh Castle in Scotland sits atop an ancient volcanic plug.
The materials ejected from volcanoes create various features and landforms that shape the surrounding landscape.
Streams of molten rock that flow from a volcanic vent during an eruption. The type of lava affects the resulting landforms:
Lava flows create features like lava plateaus, lava tubes and pillow lavas (when erupted underwater).
Material ejected explosively from a volcano, including:
Volcanic activity creates additional features beyond the main volcano structure:
Mount Pinatubo in the Philippines erupted in June 1991 after being dormant for 600 years. It was one of the largest eruptions of the 20th century.
Key features formed:
Impact: The eruption ejected 10 billion tonnes of magma and 20 million tonnes of sulfur dioxide, causing global temperatures to drop by 0.5°C for two years.
Despite the hazards, people often live near volcanoes for several reasons related to the features they create:
When the Eldfell volcano erupted on Heimaey island in 1973, it demonstrated how volcanic features can be both destructive and beneficial:
This case shows how understanding volcanic features can help communities adapt to and even benefit from volcanic activity.
Scientists monitor changes in volcanic features to predict eruptions and reduce risk:
Understanding volcanic features is essential for hazard management, as different volcano types produce different hazards. Shield volcanoes typically have less explosive eruptions with lava flows as the main hazard, while composite volcanoes can produce devastating pyroclastic flows and widespread ash deposits.
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