Lava Dome Volcano
A lava dome is a mound that will form when lava piles up over a volcano’s vent instead of moving away. Since the eruption of lava is slow there is no chance for a lava flow to occur and therefore the lava dome will form. Most of the time the sides of a dome will be steep and they are usually composed of what’s called silica-rich lava which in some cases will contain pressurized gas so that explosions can occur. The domes can be described as a small bulbous mass of lava. As the lava cools down it becomes hard and the dome forms.
Size And Shape
The size and shape of a lava dome can change from one volcano to the next. However, you can expect them to be thick and steep sided. The thickness of the lava dome can vary from up to a kilometer in height to just a few meters. The length or diameter can also vary a lot from several kilometers to just a few meters. The shape of the dome can also be very different from one to the next with some of the more common shapes being circular, flat topped, spiny, piston shaped and even a combination. The form of the dome depends on different factors including the viscosity of lava, strength and the slope of the surrounding area it is being erupted onto.
Where Do They Form?
A lava dome can form anywhere there is any volcanic activity. Usually they can be found in the crater of larger volcanoes like Mount St. Helens. However they will not only appear at the craters. In some cases the domes will form on the sides or flanks of the volcano. In rare cases they can even form away from volcanic features. It all depends on the magmatic attributes of the area around them. There are domes on Mount St. Helens which are located on its flanks. These types of domes will eventually help rebuild the mountain.
What They Are Made Of
There are different types of composition that a lava dome can have and those include anything from rhyolite to basalt. It is important to know however that most of the time the lava that will form a dome will have a higher content of silica (Si02). That composition is what makes the lava more viscous. While a dome can take one of many different types of textures, usually they tend to be blocky in nature.
Types
A lava dome can take many different shapes the first one of which is the Tortas kind. The reason for the name is the similarity that the shape has to a cake or otherwise known as a torta. This is a very common type of formation but it does happen more often in South America near the Andes Mountains.
The Peleean type of lava dome is probably the steepest of all domes. Typically they are similar to Tortas with the difference that they have smoother upper surfaces. They also have vertical spines and can collapse.
The Coulees are somewhere between a lava dome and a lava flow. This type of dome usually takes place on the side of a slope and that is why it can run down. It is rare for this type of dome to be very large but there are a few examples which are over 10 kilometers.
Finally you will be able to find what is called an Upheaved Plug which is a very interesting and very rare type of dome. The lava when it erupts tends to be stronger than that of other domes and because of that the lava is pushed up, almost like a piston. These extrusions can travel very high when compared to the surface.