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KS3 Geography - Tectonic Hazards: Volcanoes

A guide to tectonic hazards for your Year 9 course, compiled by your Librarians.

What is a volcano?

   Key fact of volcanoes:

  • A volcanoe is formed by eruptions of lava and ash.
  • Volcanoes are usually cone shaped mountains or hills.
  • When magma reaches the Earth's surface it is called lava. When the lava cools, it forms rock.
  • Volcanic eruptions can happen at destructive (convergent) and constructive (divergent) boundaries, but not at conservative (transform) boundaries.
  • Some volcanoes happen underwater, along the seabed or ocean floor.

  There are around 1511 active volcanoes in the world today.

Causes of volcanoes

   

Volcanoes happen when magma rises to the surface of the earth, which causes bubbles of gas to appear in it. This gas can cause pressure to build up in the mountain, and it eventually explodes. 

An volcano eruption occurs when pressure in the magma chamber forces magma up the main vent, towards the crater at the top of the volcanoe. Some magma will also be forced out of the secondary vent at the side of the volcanoe.

Different types of volcanoes

   Volcanoes can be described in terms of activity and can be:

  • active (erupt frequently)
  • dormant (temporarily inactive but not fully extinct)
  • extinct (never likely to erupt again)

  Volcanoes can also be grouped into four types: cinder cones, composite volcanoes, shield volcanoes and lava domes volcanoes. Mouse hoover and click over the following images to see detailed examples.

 

 

Cinder Cones Cinder cones are circular or oval cones made up of small fragments of lava from a single vent that have been blown into the air, cooled and fallen around the vent.
Composite Volcanoes Composite volcanoes are steep-sided volcanoes composed of many layers of volcanic rocks, usually made from high-viscosity lava, ash and rock debris. The eruptions from these volcanoes may be a pyroclastic flow rather than a lava flow. Mt. Rainier and Mt. Fuji are examples of this type of volcano.
Shield Volcanoes Shield volcanoes are volcanoes shaped like a bowl or shield in the middle with long gentle slopes made by basaltic lava flows. Basalt lava flows from these volcanoes are called flood basalts. The volcanoes that formed the basalt of the Columbia Plateau were shield volcanoes.
Lava Domes Lava domes are formed when erupting lava is too thick to flow and makes a steep-sided mound as the lava piles up near the volcanic vent. The eruption of Mount St. Helens in 1980 was caused in part by a lava dome shifting to allow explosive gas and steam to escape from inside the mountain. 

Impact of volcanoes

   Alaska Redoubt Erupts

      Volcanic eruptions can have a devastating effect on people and the environment. However, unlike earthquakes, volcanoes can also have positive impacts on an area. These positive impacts can help to explain why people choose to live near volcanoes.


Positive and negative effects of an eruption

Positive Negative
The dramatic scenery created by volcanic eruptions attracts tourists. This brings income to an area. Many lives can be lost as a result of a volcanic eruption.
The lava and ash deposited during an eruption breaks down to provide valuable nutrients for the soil. This creates very fertile soil which is good for agriculture If the ash and mud from a volcanic eruption mix with rain water or melting snow, fast moving mudflows are created. These flows are called lahars.
The high level of heat and activity inside the Earth, close to a volcanoe, can provide opportunities for generating geothermal energy. Lava flows and lahars can destroy settlements and clear areas of woodland or agriculture.
  Human and natural landscapes can be destroyed and changed forever.

Test your knowledge about volcanoes!

1What is a volcano?

2Where do volcanic eruptions tend to take place?

3A volcano that is flat and wide is called:

4A cone volcano is most commonly found at which type of plate boundary?

5Which type of volcano often erupts with a mix of steam, ash, rock and dust, causing a pyroclastic flow?

6Which of the statements listed below is NOT a positive aspect of a volcanic eruption?

7Which of the following is NOT a short-term response to an eruption?

8A volcano which erupts 1000 km3 of material is called:

9A supervolcano is shaped like:

10An example of a supervolcano is:

Play the Q&A game about volcanoes!


zondle - games to support learning

Animation of Volcanoes

A brief presentation about volcanoes

Pacific Ring of Fire


Chains of volcanoes and oceanic trenches form the Pacific Ring of Fire

   The Pacific Ring of Fire is a string of volcanoes and earthquakes around the edges of the Pacific Ocean. The Ring of Fire is the direct result of plate tectonics. The edges of several tectonic plates meet along the Ring of Fire, resulting in most of the active volcanoes on Earth. Today The Ring of Fire is home to over 75% of the world's active and dormant volcanoes.

Hotspots

   Most volcanoes occur near the Earth's plate boundaries, but some do not. For example, the Hawaiian islands have been formed over millions of years by volcanic eruptions thousands of miles from the edges of the Pacific plate. It is thought that a hotspot - a stationary plume of magma that rises from deep within the Earth - powers the volcanism on Hawaii. As the Pacific plate slowly moves over the hotspot, the islands in the Hawaiian-Emperor chain have been built one at a time by a numerous volcanic eruptions.

   Another hotspot is responsible for the past super-eruptions at Yellowstone National Park in the United States.

Tracking the hotspot - Yellowstone National Park

Press the green button on bottom left to watch the trail of the Yellow Stone hotspot!

Volcano safety

PLAN FOR A VOLCANO:

  • Have a disaster plan
  • Know whether or not you are at risk for danger
  • Be prepared for mudslides, flash floods, earthquakes, ash falling, acid rain and tsunamis
  •  Prepare a disaster supplies kit for your home and car. Include a first aid kit, canned food and a can opener, bottled water, battery-operated radio, flashlight, protective clothing, dust mask, goggles and sturdy shoes.
  • Know evacuation routes

DURING A VOLCANO:

  • Follow the evacuation order issued by authorities
  • Avoid areas downwind and river valleys downstream of the volcanoe
  • If your caught indoors, close all windows and doors, put machinery inside a barn, and bring animals inside.
  • If you’re trapped outdoors, seek shelter indoors. If you’re caught in falling rocks, roll into a ball and protect your head. If you’re caught near a stream, be aware of mudflows. Move to higher ground.
  • Protect yourself when ash falls. Wear long-sleeved shirts and long pants. Use goggles to protect your eyes. Wear a dust mask and keep car engines off.

AFTER A VOLCANO:

  • Cover you mouth and nose. Volcanic ash can irritate your respiratory system.
  • Wear goggles and protect your eyes
  • Keep your skin covered
  • Clear roofs of ash. The ash is very heavy and can cause the building to collapse.

Can we predict volcanic eruptions?

 

   Scientists who specialise in volcanoes are called volcanologists. They are growing more and more confident at predicting when volcanoes will erupt in the short-term. However, the further a volcano is from erupting, the harder it is to predict. Working out if a volcano will erupt in future years is still impossible.

   As a volcano becomes active, it gives off a number of warning signs. These warning signs are picked up by volcanologists and the volcano is monitored:

 
Warning signs Monitoring techniques
Hundreds of small earthquakes are caused as magma rises up through cracks in the Earth's crust. Seismometers are used to detect earthquakes.
Temperatures around the volcano rise as activity increases. Thermal imaging techniques and satellite cameras can be used to detect heat around a volcano.
When a volcano is close to erupting it starts to release gases. The higher the sulfur content of these gases, the closer the volcano is to erupting. Gas samples may be taken and chemical sensors used to measure sulfur levels.

Volcano Explorer

Play this extensive Volcano Explore game to broaden your knowledge about volcanoes.

Volcano lab

Answer 5 questions correctly to get your volcano to erupt!

Volcano activities: can we predict volcanic eruptions?

   Today, there are many active volcanoes worldwide. Is there anything we can do to predict how and when they will erupt? Use this interactive site to explore how we can forcast and cope with volcano eruptions. Switch between different topics using the links provided on the bottom, and  don't forget to try the activities listed on the left column!   (mouse click to enter