A'a lava
Volcanic rocks are igneous rocks that originated from volcanoes. In other words, these are rocks that came out of a volcano during an eruption. For example, basalt rock forms from lava flows, and pumice is often associated with explosive volcanic events. Both are volcanic rocks.
During an eruption, lava, ash and volcanic rocks can be ejected out of the vent of a volcano. Some of the largest rocks, known as pyroclastic rocks can be meters across and be ejected hundreds of meters from the vent. When a volcano is actively erupting, this material piles up around the vent of the volcano, giving it that familiar cone-like shape.
Volcanic rocks get their names from their chemical composition and texture. Basalt, or hardened lava, has a very low silica content. Another kind of volcanic rock, rhyolite, has a very high silica content. If a rhyolite lava flow cools and hardens quickly, it can form a substance called obsidian. And other lavas can have many air pockets in them, creating pumice.
Some of the oldest volcanic rocks in the world were discovered in northern Quebec, in Canada, dating back 4 billion years. This was a time when life on Earth was just getting started.
We have written many articles about the Earth for Universe Today. Here’s an article about different types of volcanoes. And here’s an article about the biggest volcano in the Solar System.
Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.
We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.
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