Exploring Southwest Iceland!
Today was another day of adventuring! On our first stop, we took a look at what had become of the old coastline of the east side of the Reykjanes peninsula. The original coastline was formed by lava flows erupted 781,000 years ago (BP), during glacial times. Over time, the glaciers melted and the coastline was lifted, due to isostatic rebound. In 1180 there was another eruption which created a new coastline. You can tell the difference from the two very easily. The older coastline is uplifted and carved by water. Presumably from an ice cap sitting atop of the rocks. It is also eroded and slightly covered in some grasses. The newer coastline is jagged and rocky, and covered in moss and lichen.
The basalts from the eruption gives us insight into the magnetic polarity of the Earth. The date of the eruption was the last magnetic polarity reversal during human existence. Since there are no environmental impact or changes to determine the reversal, the only way to tell is with rocks. By using the known, recorded date of this eruption, we can conclude when the last magnetic reversal was, and the vis versa. These rocks date ~ 774 ka BP according to their reverse magnetic polarity.
Our second stop was at a portion of the coastline that’s past the 1180 eruption. It is a beautiful area- heavily eroded- but covered in lush grasses. We examined two of the headlands and the pocket beach sandwiched between the two.
There was a small rock outcrop bordering one of the headlands. By looking at the distance of the outcrop to where the headland was now, we could see how forceful and influential the water can be at eroding. These headlands are an emergent coastline, uplifted due to isostatic rebound. Looking at the right sided headland, you can see the shield layers intermixed with pyroclastic material such as scoria. Scattering on the top of the exposed rocks along the coastlines were potholes, which indicates water flowing over the land from glacial discharge. Sheep graze on the grassy pasture along the coastline. Soils developed on the lava flows due to weathering, though not very intensive in that climate.
At stop three we looked at extensive geothermal vents. They were bubbling hot springs in a variety of colors. The underlying magma is 1200°C, hence the intense bubbling and general reactivity (Photo 8). They were grayish and chalky colored in certain places, which was pyrite. In places where it was red, it indicated oxidized iron. The springs were abundant in iron and sulfur, whose scent lingered heavily in the air.
On our next stop we explored GrindavÃkurbær, which is a large lake tucked between mountains. The lake was partially drained in 2006 when an earthquake occurred. This earthquake caused an opening in the bottom of the lake, draining the water into the groundwater reservoir beneath it. Bordering the lake are these magnificent rocks, that were beautifully eroded by wind. The rocks were layers of tephra, containing volcanic bombs and ash. It could’ve been a possible river channel after the last ice age. We thought this could be a possibility due to the appearance of water erosion as well.
Stop five we went to grænt vatn, which translates to Green Lake. Green Lake is a maar, which is a low relief volcanic crater created by a phreatomagmatic eruption. A phreatomagmatic eruption is when gases and steam from groundwater are ejected.
After that, we went to a lava tube that formed during the 1300s eruption. The tube-like structure forms by magmatic gases trapped within the moving flow when rocks cools and crystalized at the surface. The tube was thought to be a branch of the bigger, main flow. Although it’s not the main tube, the branch is thought to extend for miles. Inside the tube you could see gray stalactites hanging from the ceiling, colored gray due to the silica precipitating from the rock. The rock itself also had a reddish coating on it, and this is because of the gases from when it was active.
