We have reached our second stop, Iceland. The whole country is sliced in half by a
plate boundary, and we are here to see a great example of a divergent boundary.
At a divergent boundary, two plates pull apart from each
other, creating rift valleys and mid-ocean ridges. When Earth’s brittle surface layer pulls
apart, it usually breaks along parallel faults, tilting slightly outward from
each other. The block of earth’s crust
between the fault lines cracks and drops into the interior of the earth. The absence of that block forms a central
valley called a rift. Magma from the
center of the earth seeps up to fill that crack, forming new crust along the
boundary. When a divergent boundary is
formed between two continental plates, the rift can be from 30 to 50 kilometers
wide. When one is formed between two
oceanic plates, the rift is much narrower, only a kilometer or less across, and
runs along the top of a mid-oceanic ridge.
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http://www.cotf.edu/ete/modules/msese/earthsysflr/plates3.html |
Earthquakes can occur along the fault lines of divergent
boundaries, and volcanoes are formed where the magma reaches the surface. Iceland is splitting along the Mid-Atlantic Ridge,
the boundary between the North American and Eurasian plates. As Iceland is pulled apart, new crust is
created by the magma rising through the crack created by the divergent
boundary, but it also creates a rift along the boundary. Iceland
will inevitably break apart into two separate landmasses at some point in the
future, as the Atlantic waters eventually rush in to fill the widening and
deepening space between. The consequences of plate movement are easy
to see around Krafla Volcano, in the northeastern part of Iceland. Here,
existing ground cracks have widened and new ones appear every few months. From
1975 to 1984, numerous episodes of rifting,
or surface cracking, took place along the Krafla fissure zone. Some of these
rifting events were accompanied by volcanic activity. The ground would rise 1
or 2 meters before abruptly dropping, signaling an eruption. Between 1975 and
1984, the displacements caused by rifting totaled about 7 meters.
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| Krafla Volcano http://www.willgoto.com/1/146084/liens.aspx |
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| Icelandic Fault Line http://jscnwy.wordpress.com/iceland/ |
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