Earth’s volcanoes occur because its crust is broken into 17 major, rigid tectonic plates that float on a hotter and softer layer in its mantle. On Earth, volcanoes are generally found where tectonic plates are diverging or converging. For example, a mid-oceanic ridge, such as the Mid-Atlantic Ridge, has volcanoes caused by divergent tectonic plates pulling apart; the Pacific Ring of Fire has volcanoes caused by convergent tectonic plates coming together.
Some volcanoes are on or are Islands the size of a small island like Hawaii. Erupting volcanoes can pose many different hazards especially aircrafts in air. “Hotspots” is the name given to volcanic areas believed to be formed by mantle plumes, which are hypothesized to be columns of hot material rising from the core-mantle boundary in a fixed space that causes large-volume melting.
There are different types of volcanoes like the “shield volcano” in a shape of an elongated mountain, “volcanic cones” in the shape of a cone, “Mud volcanoes” can run 10 km in diameter and reach 700 meters high, and a “Super volcano” which is in a shape of a caldron, some volcanoes even have two heads (one head is a lot smaller than the larger head).
Dead volcanoes use to have lava/ magma until it became extinct. Active volcanoes are the volcanoes with lava/ magma. Another way of classifying volcanoes is by the composition of material erupted, since this affects the shape of the volcano. Lava can be broadly classified into 4 different compositions.
- If the eruptedmagma contains a high percentage (>63%) of silica, the lava is called Felsic.
- If the erupted magma contains 52–63% silica, the lava is ofintermediate
- If the erupted magma contains <52% and >45% silica, the lava is called Mafic.
- Some erupted magmas contain <=45% silica and produce Ultramafic lava. Ultramafic flows, also known as komatiites, are very rare; indeed, very few have been erupted at the Earth’s surface since the Proterozoic, when the planet’s heat flow was higher. They are (or were) the hottest lavas on Earth that probably had more fluid than any common Mafic lavas.
There are two types of lava according to the lava surface and they are both Hawaiian words. The first one is called A’a and the second Pāhoehoe.
- ‘Aʻa is characterized by a rough and chunky surface and is the typical texture of viscous lava flows.
- Pāhoehoe is characterized by its smooth and often ropey or wrinkly surface and is generally formed from more fluid lava flows.
In Chapters XV and XLII (15 and 42) in the book called “The Journey to the Center of the Earth” is about three people inside two different volcanoes (not at the same time).
In chapter XV Professor Hardwigg, his nephew Henry/Harry, and the eider-hunter Hans enter a dead volcano, which was very cold and dark, in Iceland. From chapters XVI-XLI they are in the dead volcano (in Iceland) that had many long tunnels that are not man-made but nature-made that were heading down to the center of the Earth. The Professor, Harry, and Hans people spend more than a month in these tunnels heading down to the center of the Earth.
They even spend about a week or more descending a set of stairs, which took them to a large grotto. One of them, somehow, got separated from the group for about three days. When Professor and Hans found Harry he was unconscious, and when Harry regained his conscience he is in a bright and airy cave that led to, what appears to be a, dinosaur world that was in the Earth/ under the Earth’s crust.
Then they spend a few weeks in that world, and then they decide to blow up a little cave that causes an Earth\quake. That sends them up a shaft at 1+ league(s) per day for about 3 days, leaving them with no food, water, and equipment.
In chapter XLI they figure out that the shaft led to inside a volcano. The volcano was an active volcano that was about to erupt. The climate in this active volcano was very hot and humid. A few minutes later the volcano erupted and it sent the Professor, Henry, and Hans out of it into the open air of Stromboli.