We may receive all the heat we need on the Earth’s surface from sunlight, but if you dig a hole just a few feet deep, you might notice that the surrounding soil is much cooler. This happens because much of the sediment is insulated from the sun’s energy. But, if you could dig miles and miles into the , you would find that the temperature of the rock would increase!

Figure 4.1. This temperature vs depth plot shows how temperature increases with depth. The rate of change is called a Geothermal Gradient. By: Bkilli1, CC BY-SA 3.0,  Wikimedia Commons.

This increase in temperature with depth in the Earth’s crust is called the . We can expect temperatures to increase about 25°C for each kilometer of depth. This sounds like a significant increase in heat, but once we pass the 100 km mark, temperatures really take off!

As we learned in the second chapter, the Earth’s iron is wickedly hot! Such heat powers , and when combined with other factors, it can lead to partial melting in the . This melted, molten rock occasionally rises to the Earth’s surface and when it does, watch out!

A will form above a chamber or plume of . There is a wide variety of volcanoes, and some are more explosive than others. Molten is far from the only hazard; volcanic eruptions can cause massive damage with ashfall, s, toxic gases, and deadly landslides. There are even a few volcanoes considered so dangerous that we call them “supervolcanoes“, and they have the potential to impact society drastically for generations.

Although volcanoes are ous, they are a continuous boon for the global economy. The precious s and useful rocks formed by volcanic processes have benefited civilization for thousands of years. In the modern economy, we use volcanism as a source of alternative energy and rocks in trades ranging from construction to cosmetics.

Learning Objectives

  • Describe the location of volcanoes in relation to plate boundaries.
  • Describe the size, shape, and eruption style of volcanoes and how they form.
  • Explain how scientists monitor and study volcanoes.
  • Identify the major volcanic hazards and their effects on humans and property.
  • Explain how volcanic processes benefit society.


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Dynamic Planet: Exploring Geological Disasters and Environmental Change by Charlene Estrada, Carolina Michele Londono, Merry Wilson is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.

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