LESSON 14.9 What are volcanoes and how are they formed?
LEARNING INTENTION By the end of this lesson, you should be able to: • identify the processes that produce volcanoes and volcanic eruptions • explain the term volcanic hotspot .
Tune in Compare FIGURE1 , which focuses on the landforms of North, Central and South America, with FIGURE3 in lesson 14.2, which shows a world map of plates, volcanoes and hotspots.
FIGURE1 Landforms of North, Central and South America (not to scale)
Mt McKinley 6194 m
Alaska Peninsula
Height in metres
ARCTIC OCEAN
4000 2000 1000
Mt Ranier 4392 m Mt St Helens 2549 m
Baffin
500 200 0
Juan de Fuca Plate
Island
Greenland
North American Plate
Pacific Plate
Iceland
Citlaltepetl 5700 m
Gulf of California
Popocatepetl 5452 m
Newfoundland
PACIFIC
Gulf of Mexico
OCEAN
Cuba
Cocos Plate
ATLANTIC OCEAN
Hispaniola
Caribbean Plate
Puerto Rico
Galeras 4276 m
Dona Juana 4150 m
Cotopaxi 5897 m
Trinidad
GUIANA HIGHLANDS
Nazca Plate
Aconcagua 6960 m
South American Plate
BRAZILIAN HIGHLANDS
Key
Antarctic Plate
Converging plate boundary
Pampas
Diverging plate boundary
ATLANTIC
Movement of plate
Tierra del Fuego
OCEAN
Scotia Plate
Source: Map drawn by MAPgraphics Pty Ltd, Brisbane
1. Describe the spatial association between mountain ranges and volcanoes. 2. What is happening to the tectonic plates at these boundaries? 3. Propose why some mountain ranges do not have volcanoes present.
14.9.1 How are volcanoes formed? A volcano is a cone-shaped hill or mountain formed when molten magma in the Earth’s mantle is forced through an opening or vent in the lithosphere. Almost all active volcanoes occur at or near plate boundaries. Some occur where two plates converge, and others occur where the plates are pulling apart, or diverging (see FIGURE1 ). There is another group of volcanoes that are formed when plates move over hotspots.
394 Jacaranda Humanities Alive 8 Victorian Curriculum Third Edition
Made with FlippingBook interactive PDF creator