Plate Margins and Active Volcanoes

Plate Margins and Active Volcanoes

• Figure 1 is a world map showing plate margins and active volcanoes.
• Active volcanoes are not exclusively found in lines along plate margins.
• Some active volcanoes occur near but not directly on plate margins.
• There are more active volcanoes around the Pacific Ocean, known as the "Ring of Fire".
• The distribution of active volcanoes along plate margins varies, with no clear pattern of more volcanoes on constructive or destructive margins.
• Active volcanoes are found on the western side of North and South America, not the eastern side.

The Structure of the Earth

• The Earth is composed of four main layers: inner core, outer core, mantle, and crust.
• The inner core is a solid and dense layer, about 1400km in diameter, composed of iron and nickel with temperatures of about 5500°C.
• The outer core is a semi-molten metal layer, about 2100km thick, with temperatures between about 5000-5500°C.
• The mantle is a semi-molten layer, about 2900km thick, which is less dense than the outer core.
• The crust varies in thickness and is made up of two types: oceanic and continental.

Crust

• The oceanic crust is thinner (5-10km) but heavier and denser.
• The continental crust is thicker (25-90km) but is older and lighter.
• Oceanic crust is continually created and destroyed as a result of plate movement, where it subducts under the continental crust.

Plate Tectonics

• The crust is broken into a number of tectonic plates.
• These plates move on top of the semi-molten mantle below.
• Current theory suggests that the movement is the result of the weight of the denser oceanic plates subducting and dragging the rest of the plate along (slab pull theory).

Plate Boundaries

• A plate boundary or margin is where two plates meet.
• There are three main types of plate boundaries: constructive, destructive, and conservative (transform).
• Constructive plate boundary: plates move apart, resulting in volcanic eruptions and earthquakes (e.g., Mid Atlantic Ridge).
• Destructive plate boundary: plates move together, resulting in volcanic eruptions and earthquakes (e.g., Nazca plate and South American plate).
• Conservative (transform) boundary: plates move past each other in opposite directions, resulting in earthquakes only.

Distribution of Earthquakes and Volcanoes

• Earthquakes occur at all types of plate boundaries, with most occurring along the Pacific 'Ring of Fire' (approximately 90%).
• Most volcanoes occur at constructive and destructive plate boundaries, with the majority located around the rim of the Pacific Ocean (approximately 75%).
• Hotspots occur away from plate boundaries and are plumes/columns of magma which escape through the Earth's crust.

Primary and Secondary Hazards

• When earthquakes and volcanic eruptions occur, there are primary and secondary hazards.
• Primary hazards of volcanic eruption: ash, pyroclastic flow, lava flow, gas emissions, volcanic bombs, lahars.
• Primary hazards of earthquake: ground shaking, gas emissions, building collapse, landslides, gas leaks, fires.
• Secondary hazards of volcanic eruption: acidification, landslides, climate change, fires, floods.
• Secondary hazards of earthquake: soil liquefaction, subsidence, mudflows, tsunami.

The Structure of the Earth

• The Earth is composed of four main layers: inner core, outer core, mantle, and crust.
• The inner core is a solid and dense layer, about 1400km in diameter, composed of iron and nickel with temperatures of about 5500°C.
• The outer core is a semi-molten metal layer, about 2100km thick, with temperatures between about 5000-5500°C.
• The mantle is a semi-molten layer, about 2900km thick, which is less dense than the outer core.
• The crust varies in thickness and is made up of two types: oceanic and continental.

Crust

• The oceanic crust is thinner (5-10km) but heavier and denser.
• The continental crust is thicker (25-90km) but is older and lighter.
• Oceanic crust is continually created and destroyed as a result of plate movement, where it subducts under the continental crust.

Plate Tectonics

• The crust is broken into a number of tectonic plates.
• These plates move on top of the semi-molten mantle below.
• Current theory suggests that the movement is the result of the weight of the denser oceanic plates subducting and dragging the rest of the plate along (slab pull theory).

Plate Boundaries

• A plate boundary or margin is where two plates meet.
• There are three main types of plate boundaries: constructive, destructive, and conservative (transform).
• Constructive plate boundary: plates move apart, resulting in volcanic eruptions and earthquakes (e.g., Mid Atlantic Ridge).
• Destructive plate boundary: plates move together, resulting in volcanic eruptions and earthquakes (e.g., Nazca plate and South American plate).
• Conservative (transform) boundary: plates move past each other in opposite directions, resulting in earthquakes only.

Distribution of Earthquakes and Volcanoes

• Earthquakes occur at all types of plate boundaries, with most occurring along the Pacific 'Ring of Fire' (approximately 90%).
• Most volcanoes occur at constructive and destructive plate boundaries, with the majority located around the rim of the Pacific Ocean (approximately 75%).
• Hotspots occur away from plate boundaries and are plumes/columns of magma which escape through the Earth's crust.

Primary and Secondary Hazards

• When earthquakes and volcanic eruptions occur, there are primary and secondary hazards.
• Primary hazards of volcanic eruption: ash, pyroclastic flow, lava flow, gas emissions, volcanic bombs, lahars.
• Primary hazards of earthquake: ground shaking, gas emissions, building collapse, landslides, gas leaks, fires.
• Secondary hazards of volcanic eruption: acidification, landslides, climate change, fires, floods.
• Secondary hazards of earthquake: soil liquefaction, subsidence, mudflows, tsunami.

This quiz assesses understanding of the relationship between plate margins and active volcanoes based on a world map. It tests knowledge of volcanic activity and plate tectonics.