Á safninu eru til sýnis fulltrúar þriggja íslenskra landspendýrategunda, þ.e. refa minka og hagamúsa. Alls finnast sex tegundir spendýra villtar á Íslandi, en það eru auk framataldra tegunda, hreindýr, húsamýs og brúnrottur. Einungis refurinn er upprunalegur, aðrar hafa flust hingað með manninum.
Uppstoppaður útselsbrimill og beinagrind úr háhyrningi eru fulltrúar íslenskra sjávarspendýra, en auk þess á stofan nokkuð af hvalabeinum sem alla jafna eru ekki til sýnis. Talsvert sýningarefni er að auki um hvali og lifnaðarhætti þeirra.
Hér að neðan er fjallað sérstaklega um hvern hóp þeirra spendýra sem finnast villt á Íslandi og umhverfis það.
Continental plates
The earth may be divided roughly into three layers: solid crust, mantle and a core. The crust of the earth is divided into continental/oceanic plates. The plates float on top of the mantle and may drift due to its movements. As the plates drift, they collide, move sideways or drift apart, as on the Mid-Atlantic ridge.
Mid-Atlantic ridge
The mid-atlantic ridge reaches almost from the Antarctic to the North pole, and is formed on the edges of continental plates that are drifting apart. Therefore volcanic activity is high on the ridge. The area where Iceland is now has been especially active, one of the so-called “volcanic hot spots” of the world. The “Ridge” cuts through Iceland in the so-called “volcanic belt”. Therefore, the west part of Iceland belongs to the North American plate while the east part belongs to the Eurasian plate. The plates drift away from each other at the speed of 1 cm/year, -theoretically enlarging Iceland by 2 cm/year.
Major rock types
Iceland is very young on geological scale. The oldest rock formations are about 16 million years old. The majority of Icelandic rocks are of igneous origin, mostly basalt. Sedimentary- and plutonic rocks such as granite are rare.
Minerals and metals
Iceland is very poor of metals, but due to high volcanic activity, it is rich of crystallised minerals such as zeolits and Iceland spar. When water runs through the bedrock, it dissolves minerals. Crystallization occurs when the water runs through holes and cavities in the bedrock, and if the space is enough, the crystals can become quite large. Temperature, pressure and trace materials may affect the structure and colour of the crystallizing minerals, resulting in a totally different structure of the same mineral such as SiO2.
The outermost part of the earth is divided into few 100–200 km thick tectonic plates, floating on top of the denser mantle. Earth’s crust is the top layer of the plates and is only 5–70 km thick.
Due to currents within the mantel, the plates move independently. At plate boundaries, the plates may therefore collide (convergent boundaries) or drift apart (divergent boundaries). Where plates drift apart, molten magma rises and creates new crust at the edges. Volcanic eruptions happen when the magma brakes all the way to the surface.
Divergent boundaries are mainly found at the ocean floor where they form ocean mountain ridges.
Iceland is atop the plate boundaries of the North- American plate and Eurasian plate, which also forms the North Atlantic ridge. Those plates drift apart at the speed of 2 cm per year.
Volcanic activity is most within the so-called drifting zone, where the plates drift apart. Border zones may also be quite active but are outside the drifting zone.
The main drifting zone is shifted in relation to the North Atlantic ridge, but connected to the ridge by two fracture sones, that are responsible for the largest earthquakes in Iceland. The shifting is believed to be the result of a pull from a huge mantel plume, also known as the Hot spot, a tremendously active and long-lived phenomenon that probably is the main reason for the existence of Iceland as we know it. Today the hot spot is located beneath the Vatnajökull area.
Icelandic eruption zones are usually characterized by fissure swarms. As those zones evolve, a central volcano may form as a result of repeated eruptions.
The layered basalt, commonly seen in the older parts of Iceland, reveals repeated lava flows from old and now inactive eruption zones.
Lava fields form when molten lava flows from a crater or fissure and cools and solidifies on the surface. Lava fields can vary from smooth to very rough, mostly depending on the type of lava.
It is estimated that eruptions have increased Icelandic lava fields of about 2,480 km2 since the settlement.
Traditionally, basaltic formations are categorized due to age (+/- 3.3 million years) in two bedrock types, blágrýti and grágrýti, tuff and modern time lava fields.
In addition to the basaltic formations, rhyolite (see below) and plutonic rocks are present, along with sedimentary rock and resent (loose) sediments. The cover of all those formations is low compared to the basalt.
When water seeps through the bedrock, it dissolves minerals. Crystallization of those minerals occurs when the water seeps through holes and cavities in the bedrock, where pressure, temperature and chemical composition of the water dictates what type of crystal will form.
Minerals
Fossils
Rhyolite
Xenoliths and spherulites
Volcanic ash and minerals
Crystallized minerals are abundant near old central volcanoes and intrusive plutonic rock formations. Crystals are most commonly found in deep, glacier eroded valleys or at the seashore where erosion is active.
Blágrýti | Basalt
Basalt columns form when tick lava flows or magma intrusions slowly cool down. As cooling occurs the solidifying rock contracts, and a net of regular cracks/polygons – usually five to seven sided, is formed horizontally on the cooling direction, each forming a single column as the cooling progresses. The name blágrýti has traditionally been used for dark basaltic formations, older than 3 million years old.
Grágrýti | Basalt
Light grey variant of basalt, younger than 3 million years old. The specimen on display is from the foundations of this house, and is a part of so called Reykjavíkurgrágrýti, a large bedrock shield of unknown origin that lies beneath most of the capital area. The age of this bedrock shield is estimated 100,000 – 200,000 years.
Móberg | Tuff
Brownish variant of basalt formed during eruptions under glacier or in the sea, where water comes into direct contact with lava. The interaction with water causes the lava to shatter into glassy fragments that later solidify into solid and rather formless rock. Most of the Icelandic Tuff formed in eruptions under glaciers in the later part of last ice age and is mostly younger than 700,000 years old. This type of rock has also been formed recently in eruptions in Surtsey, where new island in the Vestmanneyjar group was formed.
Nútímahraun | Modern lava
Lava fields formed after the last ice age, younger than 11,000 years old. Lava fields are classified by appearance into smooth and coarse. This difference is mostly due to the viscosity of the lava as slow flowing lava tends to pile up and may be extremely difficult to cross, while smooth flowing lava often solidifies with a relatively smooth but often rippled surface. In total, these lava flows cover 2480 km2, with the newest and ongoing eruption, still adding to that number.
Djúpberg | Plutonic / intrusive rock
This type of rock is formed when magma intrusions cool and solidify underground. Due to erosion and tectonic movements, rocks of this origin such as granite, are common in many parts of the world but uncommon in Iceland.
When hot water percolates through the bedrock various minerals dissolve from the rock. When the water cools down, the minerals precipitate and form secondary minerals (crystals). If interstitial cavities and fissures are present in the bedrock, the minerals can grow there and eventually fill the cavities.
The type of secondary mineral that forms depends on the temperature and pressure during formation, along with the chemical composition of the bedrock. Whithin the same cavity one may find many types of secondary minerals.
Common types of minerals in Iceland are zeolites (geislasteinar), quartz (kvarssteinar), carbonates (karbónatsteinar), high-temperature minerals (háhitasteinar), metallic minerals (málmsteinar) and clay minerals (leirsteinar).
Zeolites (Geislasteinar)
Zeolites are among the most common secondary minerals in Iceland. Between 20 and 30 different types of zeolites have been identified. Iceland is quite renowned for large and clear specimens of scolecite (skólesit).
The crystal structure of zeolites is variable in form. They are usually white or transparent with a glassy or shell-plate glaze. Mohs-Hardness: 4–5.5.
Quartz (Kvarssteinar)
Quartz is made of pure silicia (SiO²), but some varieties are impure and mixed with other chemicals that lend different colours to the crystals. The structure of quartz is quite variable in terms of size of the crystals. Jasper (jaspis) is an example of quartz with a microcrystalline structure, wheras clear quartz (bergkristall) is characterised by a macrocrystalline structure. Other types of quartz are e.g. chalchedony, onyx and agate.
The crystal structure of quartz is hexagonal. It is usually white or transparent with a glassy or shell-plate glaze. Mohs-Hardness: 5.5-7.0.
Metals (Málmsteindir)
Metals are scarce in Iceland. They are only to be found as minerals composed of metal and oxide and compounds of metals and sulphides. Iron oxides are the most common metals in Iceland, including pyrite (brennisteinskys), magnetite (magnetit) and hematite (jarnglans
Carbonates (Karbónatsteinar)
Carbonates are dominated by the carbonate ion (CO³) with one or more metals attached to it. The most common species in Iceland, and the ones that form the largest crystals, are calcite (kalsit) and aragonite (aragonit), both of which are made of calcium carbonate (CaCO³) but crystallise differently. Calcite is one of the most varied mineral on earth and exists in several thousand varieties. Mohs-Hardness: 2.2–4.5.
Calcium carbonate is the main component in the shells of many organisms, including forams, corals and molluscs. In the making of the shells, CO² is removed from the ocean, which increases the capacity of the oceans to take up CO² from the atmosphere. Therefore, carbonate minerals are not merely important as a building material for marine organisms, but also plays an important role in regulating the amount of greenhouse gasses in the atmosphere.
Iceland spar (silfurberg, CaCO³) is a transparent, water clear variety of calcite and probably the most renowned Icelandic mineral. Because of its unique optical features related to polarization of light the Iceland spar was used in physics research and manufacturing of e.g. microscopes and camera lenses. In the early 20th century, Iceland spar was mined at Helgustaðir and Hoffellsdalur, East Iceland, and exported for use in the scientific and photographic industry. The mining has now ceased altogether, and the mines are protected.
Quartz (Kvarssteinar)
Quartz is made of pure silicia (SiO²), but some varieties are impure and mixed with other chemicals that lend different colours to the crystals. The structure of quartz is quite variable in terms of size of the crystals. Jasper (jaspis) is an example of quartz with a microcrystalline structure, wheras clear quartz (bergkristall) is characterised by a macrocrystalline structure. Other types of quartz are e.g. chalchedony, onyx and agate.
The crystal structure of quartz is hexagonal. It is usually white or transparent with a glassy or shell-plate glaze. Mohs-Hardness: 5.5-7.0.
Metals (Málmsteindir)
Metals are scarce in Iceland. They are only to be found as minerals composed of metal and oxide and compounds of metals and sulphides. Iron oxides are the most common metals in Iceland, including pyrite (brennisteinskys), magnetite (magnetit) and hematite (jarnglans).
In general, secondary minerals are scarce inside the volcanic zones where relatively young igneous rocks and lavas are abundant, the exceptions being areas with geothermal activity.
In Tertiary regions, secondary minerals are common and diverse, especially in connection with central volcanos and plutonic intrusions. Usually minerals are most accessible in river gorges, steep mountain slopes or cliffs or at the shore where erosion has exposed the bedrock.
Fossilised remains of plants and animals are often to be found in fine grained clastic rock formations. When organisms fossilise, a chemical transformation occurs where organic compounds are replaced by inorganic material.
Lignite (surtarbrandur) are fossilised, compressed plant remains containing a considerable amount of carbon (~70%). Thin layers of lignite occur in the Tertiary areas of Iceland, mainly in the Westfjords. The palaeobotanical records in these sediments reflect the climatic oscillations in the North Atlantic region and indicate a slow cooling during late Tertiary. The oldest lignite horizons are 15–16 million years old, reflecting the maximum age of the igneous rock in Iceland.
A variety of lignite (viðarbrandur) is made of carbonised, flattened tree trunks. So-called year-rings, annual growth increments laid down around the outer rim of the tree trunk, are usually well detectable.
Still another variety of lignite (viðarsteinn) is fossilised wood where silicic acid (SiO²), usually jasper, has replaced organic compounds.
According to the composition of fossilised leafs and other plant remains in Icelandic lignite, it is evident that the Icelandic flora during Tertiary was similar to that in the present forests on the East coast of the USA. Thus, the climate in Iceland 15 million years ago may have been similar to what we see today along the coast south of New York. Among common species found in these early forests are alder (Alnus spp.), beeches (Fagus spp.), maples (Acer spp.), oak (Quercus spp.) and elm (Ulmus spp.). Also present were conifers like giant redwood (Sequoia sp.), mangroves (Rhizophora spp.) and firs (Abies spp.).
Fossilised animals other than molluscs are very rare in Iceland.
There are three main species of igneous rock in Iceland, depending mainly on silica (SiO²) composition: basalt (<52% SiO²); andesit (52–65% SiO²), and; rhyolite (>65% SiO²). Of these the basalt is the most common, making up 80–90% of all igneous rock, and putting Iceland among the largest terrestrial basaltic areas on earth.
Among rhyolite rocks, six different types are recognised in Iceland. Obsidian (hrafntinna) is a glassy, black rhyolite, formed by rapid cooling, e.g. at the surface of lava, or by eruptions under water. Pitchstone (biksteinn) is similar to obsidian but contains more water and is more opaque. It is usually black but sometimes greenish or brownish in colour. Perlite (perlusteinn) contains much water and has the characteristic feature of great expansion when heated.
Spherulites (baggalutar) are small, spherical rocks, sometimes fused together, formed where gas got entrapped within the rhyolite lava. Spherulites were traditionally considered to have a healing power, especially regarding the circulatory system.
Pumice (vikur) forms in swift cooling of rhyolite in Plinian eruptions. It is extremely light and floats on water. Ignimbrite (flikruberg) is the deposit of a pyroclastic flow.
A xenolith (hnyðlingur) is a rock fragment that becomes enveloped in a larger rock during the latter’s development and solidification. In geology, the term xenolith is almost exclusively used to describe inclusions in igneous rock during magma emplacement and eruption.
Lava bombs are formed from lava fragments, ejected into the air. The fragments spin and cool in the air and solidify before falling back to the ground. Lava bombs are often spherical in shape and may contain a core of previously solidified lava or sediment fragment from the lava tube beneath the crater.
Spherulites (baggalútar) are small, spherical rocks, sometimes fused together, formed where gas got entrapped within the rhyolite lava. Spherulites are harder than the surrounding rock and therefore withstand erosion much better. Spherulites were traditionally considered to have a healing power, especially regarding the circulatory system.
Although volcanic eruptions usually include lava flows on the ground and volcanic ash thrown into the air, the amount and type of the volcanic products may wary considerably. This is among other things, due to the type of magma and its concentration of gas and water.
When magma reaches the surface, the pressure drop releases gases, causing explosive activity. The coarseness of the ejecta formed by those explosions can be quite variable, ranging from lava bombs, scoria and pumice, that usually fall to the ground close to the eruption, to very fine-grained volcanic ash that may be airborne for days and cross oceans and continents.
Pele’s hair (nornahár) is formed when low viscosity lava droplets are thrown onto the air, where they are drawn into thin strands which rapidly solidify as volcanic glass. Pele’s hair is extremely fragile.
Scoria (gjall) is formed from lava, ejected from the crater. It is usually black but can also be redd, due to oxidation of iron.
When lava stars to solidify, colourful minerals may precipitate on the surface. Those minerals may be fragile and easily erodible.
Sulphur is found in various composition in nature and is an important micronutrient in living organisms. It may precipitate naturally around fumaroles in geothermal areas, forming bright yellow crystals
Steind = mineral
Gjall = scoria
Vikur = pumice
Aska = ash
Main sources:
Geology. Author: Þorleifur Einarsson. Ed. Language and culture 1985.
The Icelandic stone book. Court: Kristján Sæmundsson, Einar Gunnlaugsson and Grétar Eríksson. Ed. Language and Culture 1999.
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