Amanda is a retired educator with many years of experience teaching children of all ages and abilities in a wide range of contexts.

1. Volcanic Activity on Earth

There are around 1,300 active volcanoes in the world today, but only 20 or 30 erupt each year. Some of the major volcanoes are marked on the map below. Most volcanoes are located on or near the boundaries of the tectonic plates that make up the earth's crust.

Major Volcanic Eruptions

Mount St. Helens erupted in May, 1980. The explosion was heard more than 350 km (217 miles) away. Hot ash and gas rushed down the mountainside and 62 people were killed.

The greatest volcanic explosion occurred when Krakatoa, in Indonesia, blew up in 1883. The explosion hurled rocks 55 km (34 miles) high. The explosion was heard in Australia, and generated a 40 m (131 feet) high seismic sea wave, killing 36,000 people.

The greatest volcanic eruption was Tambora on Sumbawa, also in Indonesia, in 1815. The eruption threw up more than 100cu km (24cu miles) of ash. The island lowered by 1,250 m (4,100 feet) and 92,000 people were killed.

2. Major Active Volcanoes

3. Volcano Types and Shapes

A volcano's shape depends mainly on the type of lava that comes out of it. Thick, sticky lava forms tall, steep-sided cones. Thin, runny lava forms gently sloping lava shields and plateaux. The four main volcano types are:

• Cinder Volcanoes
• Fissure Volcanoes
• Shield Volcanoes
• and Composite Volcanoes

Let's look at each in turn.

• Cinder Volcanoes

A cinder volcano is made up of layers of volcanic ash and has a steep, conical shape. Each time the volcano erupts, another layer is added.

• Fissure Volcanoes

Not all volcanoes form over a single hole. Sometimes a crack opens up in the earth's crust, and runny lava flows out along its length, forming a plateau.

• Shield Volcanoes

When the lava that erupts from a volcano is runny, it forms a gentle slope rather than a cone. Such shield volcanoes often have many side vents.

• Composite Volcanoes

Composite cones are made of alternating layers of lava and volcanic ash.

4. Different Types of Volcanic Lava

The type of lava flow that erupts from a volcano depends on many different factors. Such factors include how much gas it contains, and whether it is erupting on to land or into the sea. The three main types of lava flow are:

• Pillow Lava

Lava erupting into the sea cools quickly in the water, forming pillow lava. Pillow lava is so called because it takes on the shape of round lumps of rock thought to look like pillows

• Pahoehoe Lava

Pahoehoe lava takes its name from Hawaiian. It is runny and fast-moving. When it cools it resembles coils of rope. Pahoehoe is based on the Hawaiian verb "to paddle" because paddles make swirling waves in the water which resembles the shapes made by the liquid lava

• and Aa Lava

The Aa type lava (from the Hawaiian verb "to burn") is thicker and stickier than pahoehoe lava. It cools to form sharp, chunky rocks

5. The Products of Volcanic Activity

The solid products of volcanic eruptions and explosions are called pyroclasts. These include cinders, volcanic ash, and large chunks of solidified lava. Cinders and ash may blanket a huge area after an eruption.

• A Volcanic Bomb

Blobs of volcanic lava erupting high into the air may fall back to earth as volcanic bombs.

• Lapilli

Fragments of cinder are called lapilli may also be formed after an eruption. The name comes from the Latin for "little stones".

• Pumice

Pumice comes from lava containing bubbles of gas. It is often so light that it floats on water. You may have a piece in your bathroom as smooth pieces of pumice are used to clean off dead skin from tired feet!

• Volcanic Dust

Dust thrown high into the atmosphere during an eruption may fall hundreds of miles away.

6. Volcanic Phases

Most volcanoes have three phases they go through in their life-times. The phases are:

1. Active
2. Dormant
3. Extinct

An active volcano has erupted in recent historic times or is still erupting. A dormant volcano has been quiet for a long time but still may erupt again at some point in the future. An extinct volcano has stopped erupting and is unlikely to erupt again.

7. The Largest Volcanic Explosions

Scientists measure the size of a volcanic explosion according to the Volcanic Explosivity Index (VEI). This grades explosions on a scale of 0 (a non-explosive eruption) to 7 or 8 for the largest eruptions. So far, no eruptions with a score of 8 have been recorded.

8. The Volcanic Landscape

Volcanic activity beneath the surface of the earth heats up water above and below the ground. This can create spectacular volcanic landscapes called hydrothermal areas, where hot water, mud, and gases gush, bubble, and steam from vents in the ground.

• Hot Springs

A steaming hot spring is formed when underground water is heated by hot rocks.As it gets hotter, the water rises to the surface.

• Bubbling Mud Pools

A pool of hot, bubbling mud may form where hot water mixes with mineral particles. Acidic volcanic gases corrode these particles from the surrounding rocks.

• Fumaroles

A fumarole is a vent that releases jets of steam and hot, volcanic gases. These gases often give off a smell of rotten eggs, because they contain sulfur.

• Geysers

A geyser is a tall jet of water that erupts when water trapped in underground chambers is heated to boiling pint by hot rocks.

• Sinter Terraces

Minerals deposited by a hot spring as it emerges onto the surface may build up into a beautiful, strangely colored formation known as a "sinter terrace".

9. Record-Breaking Volcanoes

The largest active volcano is Mauna Loa in Hawaii. It has a diameter of 100 km (62 miles).

The highest active volcano is Llullaillaco in Chile. It is 6,723 m (22,057 feet) high.

The tallest active geyser is the Steamboat geyser in Wyoming, USA. It erupts to a height of up to 115 m (380 feet).

10. Extraterrestrial Volcanoes

There exist volcanoes also on other planets and moons. Olympus Mons on Mars, which is also the highest mountain in the solar system, is an extinct volcano. Our moon also has extinct volcanoes, and evidence suggest that there may be still-active volcanoes on Venus. Io, one of Jupiter's 16 moons, has active volcanoes that throw out plumes of gases up to 160 km (100 miles) high.

A Last Word

And that brings us to the end of our exploration of volcanoes and volcanic activity. I hope you enjoyed the journey. While we know much about these things, there's always something new to find out. Scientists, both women and men, work hard all over the world to uncover new and exciting facts about the earth and its wonders. Maybe one day you could join them and become a scientist, too.

© 2019 Amanda Littlejohn

Comments

Amanda Littlejohn (author) on January 13, 2019:

Hi Zia,

Thanks for reading this article about volcanoes and taking the time to leave such a great contribution in the comments. Thanks also for your kind words about my writing. You're very kind.

Certainly it takes many years of study and training to become a scientist in any field. But with determination, there's no reason why it shouldn't be done.

Zia Uddin from UK on January 12, 2019:

Nicely done, i like your facts from the 19th century volcano eruptions. Mount Pinatubo is also another volcano in the Philliphines which had a major deadly eruption in the early nineties. I wrote a similar hub on this, but I think yours is better with more fine detail in it.

I wish I could join the scientists and become a scientist myself to uncover the depths of the world but easy said and hard to be done.