Why is lava so hot

Lava is a form of molten igneous rock which is expelled by a volcano during an eruption. When lava first emerges from the volcanic crater, it is in liquid form and can range from temperatures of 1,300°F up to 2,000°F. Lava is a very viscous liquid, having about 100,000 times the viscosity of water, which is how it flows great distances before it cools and solidifies. Lava can flow over several miles because of this viscosity, which is why some volcanoes in Hawaii have lava flows which empty into the sea.

Commonly, there are two types of lava that come to the surface of the earth. These types can come in a slow and steady lava flow, which is almost like a crack in the seam of the earth which oozes lava at a steady rate, or it can emerge from an explosive eruption, which also produces large amounts of volcanic ash. Lava expelled from the earth in this manner is not called a lava flow.
Before lava surfaces, it has the same properties below the earth, with the same viscosity and the same internal temperature. However, lava is not actually lava, until it comes into contact with the earth’s atmosphere. As long as it remains below the earth’s crust, it is known as magma. The extreme pressure from the earth’s core is what causes magma to form, and once the pressure builds up in a certain area, it must be forced to the surface in one of two types of explosions, where it becomes known as lava.

However, there are many different types of lava once the molten rock has made it to the surface. This is where the viscosity of the lava comes in, as it determines how the lava will behave. Lava which has a high viscosity tends to flow very slowly and clog, while forming semi-solid pieces which then resist flow. These types of lava also entrap large amounts of gas, which form bubbles beneath the surface which then slowly rise as the lava moves along. High viscosity lava does not flow as a liquid, but more as a semi-solid. Ironically, the high viscosity of lava is what causes it to erupt hotter than other forms of lava which have a low viscosity. Low viscosity lava flows tend to move easily and form puddles and rivers, releasing their gases as they are formed. Any eruptions are usually violent and can spew lava in many different directions. Because of this, volcanoes which contain low viscosity lava usually have large, broad cones, rather than steep mountains.

Understanding how the surface texture of lava affects both the temperature and how it behaves can go a long way to understanding what types of volcanoes are around the world. Those volcanoes which are located in the Pacific tend to be high viscosity erupting volcanoes, while those in the Mediterranean tend to be low viscosity eruptions. This means that the lava flow from volcanoes in the pacific is generally hotter than flows from volcanoes in the Mediterranean.