Impact of Volcanic Eruptions on Iceland

Massimo Fanara

1. Describe the three different types of volcanic eruptions that have given rise to rise to Iceland’s volcanic landforms.

There are three different types of volcanic eruptions based on the lava texture. These are;

• Effusive: eruptions in which lava with low viscosity and settles on the side of the volcano forming gentle slopes. In this type of eruption, gases escape easily and thus there is no explosions due to the build-up of pressure (The Geological Society, 2014).
• Explosive: occur when gas pressure builds up in the volcano until it is released catastrophically. The highlyviscousmagma magma is trapped in the volcano by a blockage, which prevents gases from escaping. As the magma rises towards the surface, pressure increases until a weak point in the blocked crater is found. At this point all the pressure is released in a massive explosion of pyroclastics, volcanic gases and lava (The Geological Society,2014).
• Mixed: Eruptions involving explosions and magma flows

2. Describe the characteristics of a thuya. How does this acquire its distinctive shape?

Tuyas are eruptions occurring underneath ice sheets resulting in a layer-cake structure with a flat-top and steep-sidedvolcano. This steep sided layer-cake shape results from the rapid cooling of lava which does not travel far from the vent and thus piles up into a steep-sided mount. When the eruption is long enough that melts all the ice, a flat cap of basaltic rock on top of the hill is formed.

3. Definethe term jökulhlaup and explain its significance to Iceland.

Jökulhlaups: refers to an outburst flood event of glacial origin. Jökulhlaups erode, deposit, and re-work sediment simultaneously; they usually cause significant glaciological and sedimentological impacts creating large canyons and transport sediment and icebergs over vast outwash plains and sandur deltas (Russell, Roberts, et al., 2005). Another important aspect of jokulhlaups is the significant heat exchange between the magma and glacier, which result in subglacial eruprions and formation of hyaloclastite ridges and tuyas (Björnsson, 2010).

4. What are the origins of Icelandic river waters? Describe the relevant main characteristics.

Most of the Icelandic river waters originate from abundant glacier melting. This result in distinctive characteristics including;

• Huge amount of debris
• High turbidity
• Usually yellowish-brown in colour.
• The maximum discharge usually occurs in July or early August.
• Most of the rivers are unnavigable.

5. Explain the following terms: (i) tephrachronology, (ii) crytotephra,and (iii) isopachs.

Tephrochronology: is a method for relating and dating geological, palaeoecological, palaeoclimatic, or archaeological sequences or events (Lowe, 2011).

Crytotephra: It involves the use of volcanic ash which travelled long distances and which may have formed distinct but invisible layers within a site’s stratigraphy (Lane, Cullen, et al., 2014).

Isopachs: Isopachs are line drawn on a map connecting all points of equal thickness of a particular geologic formation. These allow the user to create isopach mapsillustrating variations in thickness within a layer orstratum. Isopach maps are used are utilized inhydrographic survey,stratigraphy,sedimentology,structuralgeology,petroleum geologyandvolcanology.

6. One measure used totackle the problem ofsoil erosion is re-seeding with appropriate floral species. What characteristics of a plant would make it suitable for such a purpose?

Roots are important structures not only for the plant but also for the underlying terrain. Plant roots;

7. Describe one method that could be used to measure the profile of a beach.

Beach profiling can be carried out by the use of a clinometer. This method consist of first, finding two points to use as reference points which define the line to follow when measuring a beach profile. The instruments needed are a clinometer, a compass, GPS (for the starting point coordinates), a measuring tape and a piece of wood (to place the clinometer on it when taking the readings). Measurements of the beach surface are taken by the use of a clinometer which measures the angle of the slope. This is done at different intervals between the two reference points until the sea is reached.

8. Explain the following: (i) lateral moraine, (ii) kettle lake, and (iii) outwash plain.

Lateral moraine: Unconsolidated material deposited on the sides of an alpine glacier. Most of the material deposited results from the freeze-thaw weathering of alpine valley walls (Lemke, 2010).

Kettle lake: Kettles arefluvioglacial landforms created when depressions left behind by the melting of partially-buried ice blocks are filled with water (Schaetzl, n.d.).

Outwash plain: Outwash plains areplainsformed fromglacialsediments such as gravel, sand and claydeposited by meltwater outwash at the terminus of aglacier (The Geography Site, 2006).

9. Explain the presence of wave-cut platforms in areas ofIceland presently distant from the coast.

Studies were carried out on the lithostratigraphy and biostratigraphy in the northern coast of Iceland in the attempt of reconstructing deglaciations relative sea level changes. According to these studies sea level felt by approximately 45m between 11300 and 9100 BP. This corresponds to an isostatic rebound of 77m. Therefore, this change in sea level explains the presence of wave-cut platforms distant from the coast (Rundgren, Ingolfsson, 1997)

10. Distinguish between mafic and felsic lava.

Mafic lava: is less viscous than felsic lava due to lower silica content. This causes non-violent eruptions where lava moves slower. Mafic lava tends to be associated more with interplate volcanism and mid-ocean ridges and produces basaltic type rock.

Felsic lava: found mainly at convergent zones. This type of lava has a high silica and water content, causing the lava to be highly viscous and causes very violent eruptions. This lava produces rhyolite and andesitic rocks.

11. What is the nominal fix accuracy of a GPS? Why can a DGPS improve this nominal accuracy?

Nominal fix accuracy of a GPS is how accurate a GPS can be. There are several factors affecting the accuracy such as atmospheric effects, sky blockage, and receiver quality. A higher accuracy is attained when using GPS in combination with augmentation system. These enable real-time positioning to within a few centimeters (National Coordination Office for Space-Based Positioning, Navigation, and Timing, 2014).

A Differential Global Positioning System(DGPS) is an enhancement toGlobal Positioning Systemthat provides improved location accuracy, from the 15-meter nominal GPS accuracy to about 10 cm in case of the best implementations. The DGPS is a combination of local land stations connected with satellites for more accurate data.

12. In cartographic terms, explain why the datum used by a GPS navigation set must be the same as for the reference chart being used.

A datum is any numerical or geometrical quantity serving as a reference point from which to measure other quantities. With regard to chart datums, these are also used in plotting GPS positions or transferring positions from one chart to another. When plotting and transferring points from one chart to another GPS positions must be on the same datum as the chart being used in order to prevent any inconvenience regarding with hazards and safe distances.

References

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Lane, C. S., Cullen, V., White, D., Bramham-Law, C., & Smith, V. (2014). Cryptotephra as a dating and correlation tool in archaeology. Journal of Archaeological Science, 42, 42-50.

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National Coordination Office for Space-Based Positioning, Navigation, and Timing. (2014). GPS accuracy. Retrieved, 2014, Retrieved from http://www.gps.gov/systems/gps/performance/accuracy/

Schaetzl. (n.d.). Kettle lakes. Retrieved, 2014, Retrieved from http://web2.geo.msu.edu/geogmich/kettle_lakes.html

RUNDGREN, M., INGÓLFSSON, Ó., BJÖRCK, S., Jiang, H., & Haflidason, H. (1997). Dynamic sea‐level change during the last deglaciation of northern Iceland. Boreas, 26(3), 201-215.

Russell AJ, Roberts MJ, Fay H, Marren PM, Cassidy NJ, Tweed FS, Harris T. (2005). Icelandic jökulhlaup impacts: Implications for ice-sheet hydrology, sediment transfer and geomorphology. Geomorphology, 75(1–2), 33-36. doi:10.1016/j.geomorph.2005.05.018

The Geography Site. (2006). Outwash plains. Retrieved, 2014, Retrieved from http://www.geography-site.co.uk/pages/physical/glaciers/outw.html

The Geological Society. (2014). Effusive & explosive eruptions. Retrieved, 2014, Retrieved from http://www.geolsoc.org.uk/ks3/gsl/education/resources/rockcycle/page3599.html