Iceland is home to beautiful lava fields, waterfalls, caves, calderas and basalt cliffs. Calderas are formed when the surface of the earth that is volcanic active is injected with magma. This causes earths surface to be pushed up. As the magma leaves the magma chamber there is nothing left to hold up the overlying rock which results in it collapsing to where the chamber used to be in a circular shape called a caldera. There are different types of calderas. There is explosive calderas which are common to volcanoes with very viscous lava and high amounts of gas under pressure. The viscosity, or stickiness, of the lava relates to the silica content. Magma high in silica is more viscous than lava low in silica
Non Explosive calderas are dramatically less destructive. The magma feeding these volcanoes is basalt which is silica poor. As a result, the magma is much less viscous than the magma of an explosive volcano, and the magma chamber is drained by large lava flows rather than by explosive events.
The picture shows the magma chamber rising up to the serfice and erupting. This results in the roof collapsing providing us with a circular caldera.
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Iceland is home to beautiful lava fields, waterfalls, caves, calderas and basalt cliffs. Calderas are formed when the surface of the earth that is volcanic active is injected with magma. This causes earths surface to be pushed up. As the magma leaves the magma chamber there is nothing left to hold up the overlying rock which results in it collapsing to where the chamber used to be in a circular shape called a caldera. There are different types of calderas. There is explosive calderas which are common to volcanoes with very viscous lava and high amounts of gas under pressure. The viscosity, or stickiness, of the lava relates to the silica content. Magma high in silica is more viscous than lava low in silica
Non Explosive calderas are dramatically less destructive. The magma feeding these volcanoes is basalt which is silica poor. As a result, the magma is much less viscous than the magma of an explosive volcano, and the magma chamber is drained by large lava flows rather than by explosive events.
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| Magnificent look at a Iceland caldera The basalt flows in Iceland are numerous however can be seen in different forms. We will discuss A'a, pahoehoe, and pillow lava flows. A'a is characterized by a rough, jagged, spinose, and generally clinkery surface. Aa lava flows tend to be relatively thick compared to pahoehoe flows.If lava cools slowly and does not move too fast it forms smooth ropy lava called pahoehoe.
However, if it cools quickly and moves fast it can tear into clinkery pieces called a'a.
 Pahoehoe Lava happens when smooth lava surface cools to turns to a dark gray color and becomes less fluid and more viscous, behaving more like a plastic substance than a truly liquid substance. As lava continues to flow underneath this plastic skin, the surface can bunch up or wrinkle into a form that resembles coiled rope.
Pillow lavas are the most abundant type because they are erupted at mid-ocean ridges. Pillow lavas have elongate, interconnected flow lobes that are circular in cross-section.
Sources
www.geology.sdsu.edu/how.../Calderas.html
http://facweb.bhc.edu/academics/science/harwoodr/Geog102/study/volcano2.htmhttp://www.decadevolcano.net/photos/keywords/basalt.htm http://www.geology.sdsu.edu/how_volcanoes_work/Basaltic_lava.html http://en.wikipedia.org/wiki/Pillow_lava |
