Types of Volcanoes

TYPES OF VOLCANOES

There are four types of volcanoes to know about. These are called cinder cones, shield volcanoes, composite volcanoes, and lava domes.

Cinder cones are the basic volcano. Generally, just one single event ejected a lot of gas and lava into the air. The lava breaks up easily and fall to make what is called cinders in order to build a cone-shaped elevation around the vent. Many have a small crater at the top and few rise more than 1000 feet into the air. You will see lots of these in the western region of North America as part of the normal terrain. Lava flow is the last part of the event – after the eruption and formation of the cone itself. While not tall, these cones can be very wide at the base.

Composite volcanoes area also called stratovolcanoes. This is because they are layered over multiple eruptions. Their sides are steep and relatively symmetrical. Expect to see alternating layers of cinder blocks, lava bombs, and ash – rising as high as 8000 feet above their bases. Many of these are around the world, such as Mount Fuji, Mount St Helens, Mount Hood, and Mount Rainier – among others.

You will often see one or more vents with at least one crater. There will be breaks anywhere in the crater or through fissures along the side of the mountain. Lava will form dykes after it solidifies inside side vents. There is often an extensive conduit system for magma to travel upward through the mountain in one way or another.

Over time, the weathering of these dormant volcanoes will eliminate the cone, exposing magma at its base. You might see a dyke complex or a magma plug at the top to indicate that the volcano hasn't erupted in a long time.

Crater Lake in Oregon is an old crater that collapsed so much that it formed a waterfilled lake. There isn't much of an elevated cinder cone or composite volcano left except for Wizard Island near the edge of the lake. Crater Lake is essentially a caldera, which will be discussed soon. Figure 32 is an image of crater lake and its single island:

Figure 32.

Shield volcanoes are made of lava flows almost exclusively. Lava pours out everywhere as fluid from a single vent or cluster of vents near the top. They are called shield volcanoes because of their shape, where the mountain is broad and slopes gently. There is a great deal of basaltic lava in these built-up volcanoes. There are frequent rift zones where lava erupts from the sides.

Mauna Loa is currently the world's largest active volcano because its base is actually at the bottom of the ocean – about 15,000 feet beneath sea level. Above sea level, it is nearly that high as well.

In some cases, there is little elevation – just lava pouring out of vents onto broad plateaus instead of mountains. This is seen in Idaho, parts of Oregon, parts of Washington, and Iceland. Lava here is thick – as much as one mile thick in places.

Lava domes tent to be very small and bulbous in nature. The lava is too thick to do much so it piles up near the vent. This is what forms the dome shape of the volcano. Steep