Aymeric. Explorations into lava tubes in the Grand Brûlé. Lava tubes are a type of lava cave formed when a stream of low viscosity wash active continuously develops a hard crust, which is thick and forms a roof over the lava stream still flows freely. The tubes are formed in one of two ways: by crusting of lava channels and lava flows Pahoehoe where it moves beneath the surface. Lava usually leaves the point of eruption in channels. These channels are often very hot as their surroundings cool. This means that slowly develop walls around them as the surrounding lava cools and / or as the channel melts its way deeper. These channels may be deep enough to form a crust, forming an insulating tube that maintains molten lava and serves as a conduit for the flow of lava. These types of lava tubes tend to be closer to the lava eruption point. Beyond the point of eruption, the lava can flow in a unchanneled, fan-shaped outside his home, which is usually another lava tube leading back to the point of eruption. Pahoehoe call flows, these areas of the surface of cold lava movement, forming either a smooth or rough, viscous. The lava continues to flow in this way until it begins to block its source. At this point, the lava beneath the surface is still hot enough to explode at one point, and from this point the lava begins as a new "source". Lava flows from the previous source to this breaking point as lava surrounding pahoehoe flow cools. This forms an underground channel that becomes a lava tube.