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Unlock This CourseVolcanoes are openings in the Earth's crust where molten rock, gas and ash can escape from below the surface. They're some of nature's most powerful and spectacular forces, capable of creating new land whilst also causing massive destruction. Understanding volcano characteristics helps us predict eruptions and protect communities living nearby.
Key Definitions:
Most volcanoes form at plate boundaries where tectonic plates meet. When plates collide or separate, magma rises through weaknesses in the crust. The magma chamber fills up underground until pressure forces it to the surface, creating an eruption.
Not all volcanic eruptions are the same. The type of eruption depends on the magma's composition, gas content and temperature. Understanding these differences helps scientists predict how dangerous an eruption might be.
Volcanic eruptions fall into two main categories based on how violently they occur. This depends largely on the type of magma involved and how much gas it contains.
Occur when thick, gas-rich magma builds up pressure. The eruption is violent with ash clouds, pyroclastic flows and volcanic bombs. Examples include Mount St. Helens (1980).
Happen when thin, runny lava flows steadily from the volcano. Less violent but can continue for months. Hawaiian volcanoes are famous for this type.
Some volcanoes show both explosive and effusive behaviour during the same eruption period, making them unpredictable and particularly dangerous.
Mount Vesuvius is famous for its explosive eruption in 79 AD that buried Pompeii and Herculaneum. The volcano produced pyroclastic flows that moved at speeds of over 100 km/h, preserving the cities under metres of ash. Today, over 3 million people live in the danger zone around Vesuvius, making it one of the world's most dangerous volcanoes.
Volcanoes come in different shapes and sizes depending on how they've erupted over time. The type of lava and eruption style determines the volcano's final form.
These are broad, gently sloping volcanoes built by many effusive eruptions. The runny lava spreads out over large areas, creating a shield-like shape.
• Wide base with gentle slopes (usually less than 10°)
• Built from basaltic lava flows
• Multiple vents and fissures
• Generally less explosive
• Can be enormous - Mauna Loa is 120km wide
These are tall, steep-sided volcanoes built from alternating layers of lava flows and explosive volcanic debris. They're often the most dangerous type.
• Steep sides (up to 35° slope)
• Cone-shaped with a central crater
• Made of alternating lava and ash layers
• Prone to explosive eruptions
• Often found at destructive plate margins
Mount Fuji is Japan's most famous stratovolcano, standing 3,776m tall. Its perfect cone shape was formed by multiple eruptions over thousands of years. The last eruption was in 1707, but scientists monitor it carefully as over 25 million people live within 100km. Its steep sides and explosive potential make it a significant hazard.
Small, steep-sided volcanoes built from volcanic debris thrown out during explosive eruptions. They're usually less than 300m tall.
• Small and steep (30-40° slopes)
• Bowl-shaped crater at the top
• Built from loose volcanic fragments
• Usually erupt only once
• Often found on the sides of larger volcanoes
Volcanic eruptions create various hazards that can affect people, property and the environment both locally and globally. Understanding these helps with disaster planning and risk reduction.
These are the direct results of volcanic eruptions that happen during or immediately after the event.
Molten rock that flows down the volcano's slopes. Usually slow-moving but destroys everything in its path. Temperature can reach 1000°C.
Fine volcanic particles that can travel hundreds of kilometres. Causes breathing problems, collapses roofs and disrupts transport.
Fast-moving clouds of hot gas and rock fragments. Extremely deadly, moving at speeds up to 200 km/h with temperatures of 800°C.
These develop after the initial eruption and can sometimes be more dangerous than the eruption itself.
Volcanic mudflows created when ash mixes with water from rain or melted snow. Can travel far from the volcano and bury entire towns. The 1985 Nevado del Ruiz eruption in Colombia created lahars that killed over 23,000 people.
This relatively small eruption had massive global impacts. The ash cloud disrupted air travel across Europe for six days, cancelling over 100,000 flights and affecting 10 million passengers. The fine ash particles could damage aircraft engines, showing how volcanic hazards can have far-reaching consequences beyond the immediate area.
Volcanoes aren't randomly distributed around the world. They follow clear patterns related to plate tectonics, with most occurring along the edges of tectonic plates.
About 75% of the world's active volcanoes are located around the Pacific Ocean in an area called the Ring of Fire. This region is extremely active because several tectonic plates meet here.
• Stretches from New Zealand to Chile
• Includes Japan, Philippines, Indonesia
• Contains 452 volcanoes
• 90% of world's earthquakes occur here
• Home to many explosive stratovolcanoes
Some volcanoes occur away from plate boundaries at 'hotspots' where plumes of hot material rise from deep in the Earth's mantle.
The Hawaiian islands were created by a hotspot under the Pacific Plate. As the plate moves northwest, new islands form whilst older ones become extinct. This explains why the Big Island has active volcanoes whilst older islands don't.
Scientists use various methods to monitor volcanoes and try to predict eruptions. This helps protect communities and reduce the impact of volcanic hazards.
Before most eruptions, volcanoes show warning signs that scientists can detect with modern equipment.
Increased earthquakes as magma moves underground. Seismometers detect these movements days or weeks before eruptions.
The volcano's shape changes as magma pushes upward. GPS and satellite measurements can detect tiny changes.
Changes in the type and amount of gases released. Increased sulfur dioxide often indicates rising magma.