Types of volcanoes

• The magma chamber is the source of lava, ash, and gases.
• Volcanic eruptions can be explosive or effusive depending on the viscosity of the magma.
• Explosive eruptions occur when gas bubbles expand rapidly due to high pressure, causing an explosion that ejects solid fragments into the air.
• Volcanic eruptions can be explosive or effusive.
• Explosive eruptions occur when gas bubbles expand rapidly due to heat, causing an explosion that ejects rock fragments into the air.
• Explosive eruptions occur when gas bubbles expand rapidly due to low pressure, causing violent explosions that eject large amounts of material into the air.
• Effusive eruptions are less violent than explosive ones and involve slow-moving lava flows.
• Effusive eruptions are less violent than explosive ones and involve slow-moving lava flows.
• Effusive eruptions are less explosive and involve slow-moving lava flows.
• Lava flows from fissure vents, which are cracks in the ground through which molten rock pours out during an eruption.
• Effusive eruptions are less violent than explosive ones and involve the slow flow of lava from fissures or vents.
• Lava flows during effusive eruptions may form cinder cones, shield volcanoes, or flood basalts.
• Lava flows during effusive eruptions are typically basaltic and have low silica content.
• Cinder cones are small, steep-sided volcanoes formed by the accumulation of loose rock fragments (cinders) expelled during explosive eruptions.
• Effusive eruptions are characterized by low-viscosity magmas with slow flow rates and minimal fragmentation.
• Effusive eruptions are less violent than explosive ones but still release large amounts of material onto the surface.
• Lava flows from fissures (cracks) in the ground during effusive eruptions.
• A volcano is a mountain where lava (hot, liquid rock) comes from a magma chamber under the ground
• Volcanoes usually have a summit, a slope, and a base
• Most volcanoes have a volcanic crater at the top, where materials pour out when they are active
• Materials that can pour out of a volcano include lava, steam, gaseous compounds of sulphur, ash, and broken rock pieces
• Volcanoes erupt when magma and pressure come together, blowing off the top of the solid rock and allowing magma to pour out
• Shield volcanoes are built out of layers of lava from continual eruptions without explosions
• The lava from shield volcanoes is very fluid, spreading out over a wide area and giving the volcano gently sloping sides
• Shield volcanoes do not grow to a great height, but can still be huge, like Mauna Kea in Hawaii
• Mauna Kea in Hawaii is the biggest mountain on Earth, even taller than Mount Everest if measured from its base on the floor of the sea
• Stratovolcanoes, also known as composite volcanoes, are tall, conical volcanoes built up of many layers of hardened lava, tephra, pumice, and volcanic ash
• Stratovolcanoes have a steep profile and periodic eruptions
• The lava from stratovolcanoes cools and hardens before spreading far, it is sticky with high viscosity
• The magma forming the lava of stratovolcanoes is often felsic, with high-to-intermediate levels of silica, and less mafic magma
• Big felsic lava flows from stratovolcanoes are uncommon, but have travelled as far as 15 km (9.3 mi)
• A caldera is formed when a huge stratovolcano erupts and blows its top off
• Leaves a crater where the top of the volcano used to be
• Krakatoa, famous for its 1883 eruption, is now much smaller
• Two main processes form volcanoes:

  • When two tectonic plates come together, one plate (usually the oceanic plate) goes under the continental plate in a process called subduction
  • The subducted plate melts and forms magma inside the magma chamber, leading to pressure buildup until the magma erupts through the Earth's crust
• The second way volcanoes are formed is when a tectonic plate moves over a hot spot in the Earth's crust

  • The hot spot works its way through the crust until it breaks through, forming features like the caldera of Yellowstone Park and the Hawaiian Islands
• Volcanoes can be classified based on their pattern of eruptions
• Active volcanoes are currently erupting or have erupted in the last 10,000 years
• Example: Mount St. Helens in the United States is an active volcano
• Dormant (inactive) volcanoes are currently quiet