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A lava field, also called a lava plain or lava bed, is a large expanse of nearly flat-lying lava flows often composed of highly fluid basalt lava.
The lava field you can discover with this earthcache is called Illahraun. Reveal the fascinating geology of Iceland!
GENERAL INFORMATION ABOUT LAVA FIELDS
A lava field, also called a lava plain or lava bed, is a large expanse of nearly flat-lying lava flows. Such features are generally composed of highly fluid basalt lava, and can extend for tens or even hundreds of miles across the underlying terrain. The extent of large lava fields is most readily grasped from the air or in satellite photos, where their typically dark, nearly black color contrasts sharply with the rest of the landscape.
The area around lava fields is marked by active volcanism under its surface and therefore allows only little vegetation. This can also been seen by in hot springs or sulphur springs and thus, also lakes.
Lava is the molten rock expelled by a volcano during an eruption. The resulting rock after solidification and cooling is also called lava. The molten rock is formed in the interior of some planets, including Earth, and some of their satellites. The source of the heat that melts the rock within the earth is geothermal energy. When first erupted from a volcanic vent, lava is a liquid at temperatures from 700 to 1,200 °C (1,292 to 2,192 °F).
A lava flow is a moving outpouring of lava, which is created during a non-explosive effusive eruption. When it has stopped moving, lava solidifies to form igneous rock. The term lava flow is commonly shortened to lava. Although lava can be up to 100,000 times more viscous than water, lava can flow great distances before cooling and solidifying because of its thixotropic and shear thinning properties. The result of these flows are called lava fields. The word "Lava" has a Latin origin. "Labes" means fall or slide.
Source: Wikipedia and www.gold-mueller.de
TYPES OF LAVA
There are several types of lava which can be found around the world. The two most encountered forms are ʻAʻā and Pāhoehoe.
ʻAʻā is basaltic lava characterized by a rough or rubbly surface composed of broken lava blocks called clinker.
The loose, broken, and sharp, spiny surface of an ʻaʻā flow makes hiking difficult and slow. The clinkery surface actually covers a massive dense core, which is the most active part of the flow. As pasty lava in the core travels downslope, the clinkers are carried along at the surface. At the leading edge of an ʻaʻā flow, however, these cooled fragments tumble down and are buried by the advancing flow. This produces a layer of lava fragments both at the bottom and top of an ʻaʻā flow.
Pāhoehoe (from Hawaiian meaning "smooth, unbroken lava"), also spelled pahoehoe, is basaltic lava that has a smooth, billowy, undulating, or ropy surface. These surface features are due to the movement of very fluid lava under a congealing surface crust.
A pāhoehoe flow typically advances as a series of small lobes and toes that continually break out from a cooled crust. It also forms lava tubes where the minimal heat loss maintains low viscosity. The surface texture of pāhoehoe flows varies widely, displaying all kinds of bizarre shapes often referred to as lava sculpture. With increasing distance from the source, pāhoehoe flows may change into ʻaʻā flows in response to heat loss and consequent increase in viscosity. Pahoehoe lavas typically have a temperature of 1,100 to 1,200 °C (2,010 to 2,190 °F).
Most lava flows on the Earth are less than 10 km (6.2 mi) long, but some pāhoehoe flows are more than 50 km (31 mi) long.
THE LAVA FIELD ILLAHRAUN
The lava field Illahraun is a not a standard example of a lava field, but contains some specialities which you can discover here.
It originated in the year 1226 and therefore is relatively young. It is about 200 m above sea level. Illahraun is the islandic word for "Lava of horror". The lava is the result of volcanic activities from several vulcanos in this region. The most important ones are Hrútagjá, Þráinskjöldur and Sandfellshæa. Together with these three volcanos, there are six smaller ones in the nearby vicinity which are all about 10,000 to 15,000 years old. This strong activity and constant eruptions cause the whole region to increase or decrease its height at the same time. Most lava fields are sloped, as the lava slides down the volcano, gets colder during this process and forms the stones we see today. Illahraun is special in this.
The lava at Illahraun cooled down quite quickly in comparison to many other lava fields. A reason for that is that there is no single volcano which could erupt more and more magma to re-heat the already outflown lava. The lava at Illahraun quickly lost its speed and cooled down. In comparison to other volcanic regions like Hawaii or Indonesia, this is a special characteristic.
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To log this earthcache, please answer the following questions:
1) The listing describes two forms of lava. Which form is the Illahraun lava field? Give reasons for your answers.
2) Is the lava field generally sloped or is it flat? Explain the reason for this by thinking of the multiple volcanic activities in southwestern Iceland.
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Have fun discovering the wild geology of Iceland!
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