Glaciers in Iceland?

Question

I recently when to visit Iceland on Holiday.

We went to a Glacier and found water was bubbling close to it. In a fairly ferocious way. Why is this??

Also, why is Geysir inactive? and what makes Geysir and Stokkur erupt??

Answer 1

Iceland is a very volcanically active country. The island itself is formed out of the ridge where the North American and Eurasian continental plates are gradually pulling apart - if you visit Thingvellir, you can walk right across the join from one tectonic plate to the other. Hot molten rock wells up into the gap as the plates pull apart and solidifies, forming new rock, so in geological terms the island is very young. With all this geological activity going on, the ground beneath Iceland is very hot. Any water that flows through the ground gets heated vigorously, which is why the country has lots of geysers and natural hot springs. In fact, the country has more heat energy coming up from the Earth's mantle than they know what to do with - they generate most of their electricity from the natural hot water, pump cheap hot water to all the homes there, and even pump hot water underneath the roads and pavements to keep them ice-free.

Geysers, of which Strokkur and Geysir are the best known, are formed from narrow channels in the rock connected to large underground reservoirs of water. Water from deep underground (over a mile down) gets heated up by the hot rocks at that depth and rises. Meanwhile, the water close to the surface cools off in the air, becomes denser and tries to sink down, but because the opening is narrow and more hot water is trying to bubble up from below, it can't move easily, so it acts like a kind of "cap", holding the hot water in. The pressure and temperature of the reservoir keeps increasing until it becomes too much for the surface water to hold back, when it erupts in a huge jet of superheated water and steam. This lets the reservoir cool off again, and the process starts anew.

While many geysers are predictable, like Strokkur's eruption every five minutes or so, others are less predictable. The ground below the geysers can change and shift around, often in response to earthquakes, which can block or open channels and reservoirs and completely change a geyser's behaviour. 100 years ago the Great Geysir used to erupt several times a day, but this decreased to almost completely dormant by the 1920s. Because it is such a tourist attraction, various attempts have been made over the years to force it to erupt, including digging a channel and even throwing soap powder in (to break the water's surface tension and hasten an eruption), but by the 1990s even these measures were ineffective. In 2000 there was an earthquake which shifted some rock underground and started Geysir erupting again, up to eight times a day, but once again the frequency declined and eruptions are infrequent now. Because the geology of geysers is difficult to monitor and changing all the time, their behaviour is impossible to predict - Strokkur could stop tomorrow, or Geysir could suddenly burst into life again, or a new geyser could pop out of nowhere. (A story I was told when I was in Iceland recalled a family who found the dining room in their house unusually hot one day, then the next day a hot spring erupted through the floor!)