Where the Eurasian and North American tectonic plates meet.
Iceland is a rather young country, at least in geological context. Because of this the island is very active when it comes to volcanic and geothermal activity. Great example of this is in Thingvellir, in the southern part of Iceland, where the North American and Eurasian tectonic plates meet or rather move away from each other. This can easily be seen on land in Thingvellir, which is a national park. The great forces of the tectonic plates can be seen in the unique surroundings in Thingvellir and were among the criteria that resulted in Thingvellir being listed on the United Nations World Heritage list.
A tectonic plate is a massive plate that consist of solid rock. A tectonic plate floats loose from other tectonic plates but comes close to them and interacts with them where their edges meet, like underneath Iceland. The continents are stuck on tectonic plates and move along with them. Interactions of tectonic plates are believed to be the main reason of most earthquakes and volcanic activity on the Earth. This continues constantly and Iceland get to feel the consequences because of the island location on the Mid-Atlantic Ridge.
The western side of the Eurasian and eastern side of the North American tectonic plates form the northernmost part of the Mid-Atlantic Ridge which Iceland is located on. In a sense, it can be said that Iceland is a kind of bridge between continents due to this unique location on the Mid-Atlantic Ridge. This results in the aforesaid volcanic and geothermal activity. Many of the Volcanic eruptions in Iceland are caused by the Eurasian and North American tectonic plates moving apart, recent example of this is the eruption of Eyjafjallajökull in April 2010 which disrupted air travel across large parts of Europe.
Another eruption caused by the tectonic plates moving apart is the eruption in Bárðarbunga volcano and Holuhraun in 2014, which is connected to Bárðarbunga by underground canals. It is believed that a process of the tectonic plates movement has begun and will last for quite some time. This process will most likely result in more eruptions in Bárðarbunga and the connected volcanic system.
The tectonic plates make landfall in the Reykjanes Peninsula and stretches towards Thingvellir and further northeast and east. Iceland is the only inhabited island in the world where tectonic plates and ocean ridge are visible on land. This makes Iceland a real hotspot in geological context. This results in many active volcanoes, e.g. Hekla and Katla. The influence of the tectonic plates also stretched eastward to Vatnajökull which is the third biggest glacier in Europe. Underneath the Vatnajökull glacier are several volcanoes and some of them are active and erupt occasionally.
Earthquakes are rather frequent in Iceland but they are often result of the movements of the tectonic plates. Earthquakes can affect how water flows to many of the hot springs in Iceland. This was the case in June 2000 when two large earthquakes hit the southern part of Iceland. Because of them the Great Geysir begun to erupt hot water again after being almost inactive for half a century.