Shield Volcanoes, the least dangerous type of volcano, are named for their shape which resembles that of a shield laid down onto the earth. They are wider and have a dramatically less steep slope than that of a cone volcano, as shown here:
Eruptions for shield volcanoes are not isolated, but rather occur over several points on the fractured volcano, as illustrated in the following diagram:
Iceland is home to approximately 130 volcanoes of various types. It is located over the Mid-Atlantic ridge, where the North American and Eurasian plates meet.
Skjaldbreiður, aptly named and meaning broad shield in Icelandic pictured below, erupted nearly 9,000 years ago. Shield volcanoes have slow moving effusive eruptions, where lava is poured out onto the ground. This eruption created lava fields and the basin for Þingvallavatn, Iceland's largest lake. Silfra is a fissure extending from Þingvallavatn, totaling at about 300 meters long.
Glaciers would melt from a river directly into Þingvallavatn, but the eruption of this shield volcano blocked the river. Now, for several meters, the melted glacial runoff is filtered through the porous lava rock. This filtration system is why Silfra has become such a scuba haven, offering some of the clearest diving waters and highest underwater visibility ever known.
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