1.4

• What causes volcanic eruptions?

  Volcanoes are fractures in the Earth's crust through which lava, ash, and gas erupt. They are associated with plate margins, where pressure builds as plates move, causing magma and gases to rise to the surface.
• What happens when magma reaches the Earth's surface?

  When magma reaches the Earth's surface, it is called lava. As lava cools, it forms rock, and as volcanoes erupt, they grow larger.
• How many volcanoes are currently considered active?

  There are 1,900 volcanoes now considered active, which are likely to erupt.
• How many people have died from volcanic eruptions since 1800?

  Since 1800, approximately 260,000 people have died from volcanic eruptions.
• What was the impact of the Eyjafjallajökull eruption in April 2010?

  The eruption caused atmospheric ash clouds that affected flights over Northern Europe for a week. 100,000 flights were cancelled, affecting 10 million people. Airlines lost $1.7 billion in revenue. Global airline capacity was cut by 30%, and European capacity was cut by 75%. Kenya's economy lost $1.3 million daily in revenue from lost flower and vegetable exports.
• What are primary hazards of volcanic eruptions?

  Lava flows: Can reach 1170°C, moving slowly but destructive when fast-flowing. Pyroclastic flows: Fast-moving, destructive mix of dense rock, ash, and gases. Ash and tephra falls: Volcanic rock fragments and ash that can travel thousands of kilometers, causing poor visibility, slippery roads, and damage to structures. Gas eruptions: Dissolved gases like water vapor, CO2, and sulfur dioxide released during eruptions, which can travel great distances.
• What are secondary hazards of volcanic eruptions?

  Lahars: Flows of rock, mud, and water down volcanic slopes, often triggered by melted snow or heavy rainfall. Jökuhlaups: Sudden releases of water, rock, gravel, and ice when heat from an eruption melts snow and ice.
• When did the Montserrat eruption occur, and what was its impact?

  the Soufriere Hills volcano erupted on July 18, 1995, continuing for five years with the worst eruption in 1997. Pyroclastic flows affected most of the island, and only a small amount of lava erupted. 2/3 of the population (11,000) were evacuated, mostly permanently. The capital city was destroyed, 2/3 of houses were buried or flattened, and ¾ of infrastructure was destroyed. The tourist industry collapsed, leading to job losses. Farmland and rainforests were destroyed, and many young people emigrated, leaving behind an aging population.
• What are volcanic hotspots?

  Hotspots form in the middle of a tectonic plate, where rising plumes of magma erupt on the ocean floor to form volcanoes. As the plate moves over the hotspot, the volcano is carried away, and a new volcano replaces it. This creates a chain of volcanoes, such as the Hawaiian Islands.
• How do we measure the magnitude of volcanic eruptions?

  The Volcanic Explosivity Index (VEI) is used to measure the magnitude of eruptions on a logarithmic scale from 0 to 8. It is based on: Volume of tephra and ash, Height of material ejected into the atmosphere, Duration of the eruption and Observations of eruption activity
• How are volcanic eruptions predicted?

  Seismometers: Detecting seismic activity. GPS and satellite-based radar: Monitoring changes in the shape of the volcano. Rising magma and tilting: Indications that an eruption may occur soon.