Our visit to some of the youngest land on the planet really was a great experience. From the moment of touchdown at Keflavik Airport we crossed the lava field to Reykjavik, saw the new roads being bulldozed over the basalt and the buildings going up, it was a sight to start the camera clicking.

Iceland sits astride the Mid Atlantic Ridge where the remains of a mantle plume trails across the area of the North Atlantic Igneous Province and splits down the centre as the plates spread. The N.A.I.P dates back to around 62 million years when a large plume raised the ocean floor and created a long plateau which can be traced around 2000km from Greenland to Scotland. The two sides of the rift on the island are not an exact mirror image of each other as the south west Snaefellsnes peninsula is still an active area so the older basalts here have not cooled and subsided as much as those in the north west and south east.

Iceland started to form about 25my ago and it took about 8my to emerge from the ocean.

Age map showing spreading axes along active rift zones.

Newest Rocks Last Ice Age to Present

Next Oldest 3MA to Last Ice Age

Oldest Rocks 16MA - 3MA

The active spreading zones vary from 20-50 Km wide and the magma flows and erupts both from volcanic centres and long fissures. As the rift spreads it controls the directions that most of the lava moves so maintains the very distinctive NNE-WSW trend of all the features in the landscape. After about 7my the rift and active zone shifted with a northern zone starting and the latest move towards the SE created the eastern rift about 3My ago. Iceland is unique in having a mix of basalt flows from the fissures, rhyolites and other silicic material which give large ash falls and can finish with caldera collapse and also the strange "moberg" basalt in the subglacial eruptions. The very distinctive shield volcanoes have primitive olivine magmas and are considered to be "one stop" events. In addition to the spreading zone at the rift the whole N Atlantic Oceanic plate is moving NW about 2cm/yr. The plume is now about 200km S/E from the plate boundary and under the Vatnajokull glacier!

About 3/4 of the exposed rocks are solid igneous with the rest reworked volcanically or glacially into sediments. The amount of mixing of material in the magma chambers can be judged as you look at the stark black rows of fissure cones and recent lava flows and contrast them with the multicoloured flows on the craters and ash falls.

The overall effect, bright blues, reds, oranges and creams of the geothermal pools, vivid green on the rich volcanic soil areas all surrounded by black beaches and white surf, was much more colourful than we expected. The first visit was to Pingvellir situated in a graben which marks the West Volcanic Zone rift. The rivers and lakes are enclosed by assorted moberg ridges, table mountains and the shield volcano Skjaldbreiour. The rift runs up to 8km long and can be up to 60m wide. Ice sheets have come and gone many times and each time altered the size of the lake as they have done to most of Iceland's water and river systems. The floor of the rift is still subsiding and the track through the rift exposes the internal structure of the lobes and sheets as the lava flowed.

"Son of Geysir"

The real show started as we arrived at Geysir. The original spring is now a silent crust of silica sinter and has been replaced by Strokkur a few meters away down the slope. The whole cycle is impressive as the water drains back into the hole a short wait leads to a bubble and dome which rises and falls as the steam pressure builds and then with a scream the fountain erupts and spray blows in the wind. The water runs away and leaves the minerals and coloured deposits all down the hill side. There are several other smaller springs and pools around each doing "their own thing" and providing a great show.

Icy water above ground provided the next spectacular at Gullfoss waterfall. Glacial river Hvita is cutting back the gorge at a rate of 25cm/year and in two steps over basalt sills drops 32M. A stop at a camp site on the way up to Akureyri gave another opportunity to walk around a small geothermal springs area and watch the warm water build its delicate white lace silica terraces down the hillside.

Gullfoss Waterfall

The next day was spent locally as we made the shorter move on to Myvatn and after the long haul the day before rather welcome. Krafla volcanic system has a caldera and also a fissure zone which extends over 100km up to the north coast. The caldera is over 200 000 years and 10km wide and has grown in various stages with both subglacial and subaerial eruptions. Walking over the latest lava from the 1977-84 activity was hard going. There was sulphur in the air and in lots of places steam and hot air was rising through the fresh lava flows. Electricity is produced from this geothermal area and we were also able to sample the "Baby Blue Lagoon" which was new for the season in this area.

Up to Husavik to go whale spotting. The harbour has been formed on the side of a major fault in the Tjornes Fracture Zone. The valley running off shore is 5-10km wide and 3-4km deep. Total movement in about 9 million years of nearly 60km along the fault accommodates movements in the rift parallel to the spreading zone and also uplift after the ice sheet melted. This in turn allows the magma plume to rise and keep the cycle active. The old fishing boat was a great craft and we did spot a few minkie whales.

Further north along the coast we had a chance to see some "proper sediments". The Tjornes beds with marine fossils record a time with a warmer climate from late Pliocene times when a near shore environment and shallow seas at least 5ºC warmer was present. Molluscs and pollen from lignite seams reveal that coniferous as well as broad leaf trees were growing. Not far above these lava flows are interspersed with tillites as the ice returned.

Asbyrgi was also a complete change as we turned off the lava fields into an oasis where the 100m high cliffs were obscured at lower levels with light vegetation. 2500 years ago a glacial burst from under Vatnajokull glacier, crashed over the lava flows a distance of 170km north to the sea and gouged out the basin on the way. Not far away Dettifoss waterfall is wearing its way up stream with torrents of grey muddy water.

Before we left Lake Myvatn a trip round the margins included walking around the mysterious "rootless cones", exploring the twisted lava remains of the lake of impounded lava at Dummuborgir and a view of the big tuff cone of Hverfjall. All this area formed within the last 3000 years and the lava advancing across the lake floor built the rootless cones as the steam created the explosive vents in its wake. Dummuborgir was a lake of lava that filled and emptied several times as flows were blocked and released. At Grotagja a section across the plate boundary is marked with a long hot water filled tunnel under a cracked lava field.

Fig. I - Formation of "Rootless Cones"

(a) Lava has covered the basin and is moving in lava tubes. These break, lava gets into wet sediment below - rootless eruptions.

(b) A fully developed rootless-cone group.

A long day was needed to reach the Askja volcano complex in the central highlands. Over several hundred thousand years activity the 200km long by 20km wide volcanic area is the longest in Iceland. Table mountains on the system have a combination of sub glacial and subaerial flows and the ice at the time is reckoned to have been 800m deep. Approaching the volcano the area is increasingly blanketed in pale coloured pumice from the 1875 eruption. The latest lava dates from 1961. The main crater is 8-10km across and houses the smaller craters formed when the caldera collapsed around 1876. The activity rumbled on till the late 1930's.

Askja volcanic craters

Fig II - Sub-glacial eruptions

(a) Pillow lava ridge

(b) Moberg Ridge

(c) Table Mountain once ice is breached.

Arriving on the East Coast the scenery carved through Tertiary Basalt flows by the glaciers looked very similar to our Lake and Scottish scenery. It was possible to see some of the many dike swarms which had built the lava mountains. The remainder of the tour was around the south east coast and took us over the vast sandur plains. These plains build out as the melt waters from the Vatnajokull glacier recycle the eroded lava. Every few years glacial outbursts from eruptions under the ice demolish the road and bridges. Twisted girders from the 1996 flood can be seen dotted across the black sands. The recent new eruptions under the ice in this area mark the position of the plume.

All the adverts for trips to Iceland show the grounded icebergs in the Skaftafellsjokull glacial lagoon and on a perfect still sunny morning the sight was just amazing. A whole spectrum of colours from black blocks from the dusty edges of the ice to greeny-blue reflections in the white bergs, all of which were in turn mirrored in the water. Nobody said much we just stood and looked!.

Grounded icebergs at Skaftafellsjokull

Many web sites have lots of details about the geology of the island and will repay some exploration.

References

Iceland. Thor Thordarsson & Armann Hoskuldsson. Pub. Terra Publishing ISBN: 1-903544-06-8.

The Cretaceous World. Ed. Peter Skelton. O.U. Pub. Cambridge University Press. ISBN: 0 521 53843 2.