The Earth’s mantle, just a few dozen kilometers beneath your feet is incredibly hot. The high temperatures cause rocks to melt and form magma that collects in vast chambers beneath the Earth’s surface. Since it’s lighter than the surrounding rock, this magma makes its way up through weaknesses in the rock until it reaches the Earth’s surface erupting as a volcano. The spot where it erupts is known as a volcanic vent.
A volcanic vent is that spot in the Earth’s crust where gases, molten rock, lava and rocks erupt.
Volcanic vents can be at the top of some of the largest volcanoes on Earth, like Hawaii’s Mauna Kea, or they can be openings in the Earth’s crust down at the bottom of the ocean. The shape of the volcanic vent can sometimes define whether the volcano is explosive or not. A fissure vent can be a few meters wide and many kilometers long. Lava pours out of fissure vents, creating lava channels, but they don’t usually explode.
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The tall familiar cone shaped stratovolcano (like Mount Fuji) can have one volcanic vent at the top of the mountain, but also have many smaller volcanic vents across the flanks of the volcano where smaller eruptions occur. These large volcanoes can erupt explosively, posing a great danger to people living nearby.
In the case of very viscous (or thick) lava, you can get a slow buildup of material into a lava dome. The lava is so thick that it doesn’t move very far from the volcanic vent. Instead it just plugs it up, forming a bulging dome of material. These can also explode violently.
We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.