earth science

Hengill

Hengill is a earth science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Hengill rather than just read about it. In short: Hengill (Icelandic pronunciation: [ˈheiɲcɪtl̥] ) is a volcanic table mountain situated in the south-west of Iceland, to the south of Þingvellir. The volcano is still active, as evidenced by its numerous hot springs and fumaroles, but the last eruption occurred approximately 2,000 years ago, before the settlement of Iceland.

Key takeaways

Hengill belongs to earth science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Hengill to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Hengill from memory before moving on to harder problems.

Reference excerpt

Hengill (Icelandic pronunciation: [ˈheiɲcɪtl̥] ) is a volcanic table mountain situated in the south-west of Iceland, to the south of Þingvellir. The volcano is still active, as evidenced by its numerous hot springs and fumaroles, but the last eruption occurred approximately 2,000 years ago, before the settlement of Iceland.

Geography The mountain is south of Lake Thingvallavatn (Þingvallavatn in Icelandic), south-west of the Nesjavellir geothermal area, south of Þingvellir National Park and is the most prominent part of a volcanic region that extends to the coast. South of the mountain towards the coast is the Hellisheiði geothermal area to its south-west, and the town of Hveragerði on Iceland's main ringroad, Route 1 about 45 km (28 mi) east of Reykjavík. At the coast is the port of Þorlákshöfn.

Geology The mountain is part of the 60 km (37 mi) long Hengill volcanic system, which is part of the Reykjanes volcanic belt, and is a hyaloclastite massif of tuyas and tindars. The dominant lava in the Hengill volcanic system is tholeiitic basalt, but andesite and about 20 km2 (7.7 sq mi) rhyolite occur within the central mountain. The largest lava shield covers about 50 km2 (19 sq mi). Four small lava shields are picrite basalt and one lava shield contains about 3 km3 (0.72 cu mi)of olivine tholeiite. It is located at the intersection with two other tectonic volcanic systems, the West volcanic zone of Iceland and South Iceland seismic zone, and is co-located to the plate boundary between the North American, Eurasian and Hreppar plates. This intersection is called the Hengill triple junction. Hveragerdi to the south is a volcano in the volcanic system that became extinct 300,000 years ago, but still has significant seismic activity. It can be regarded as a predecessor volcano. This seismic activity is significant not only because of human impact but also because the earthquakes are grouped along faults striking north–south or east–west, but not north to north-east, as might be supposed based on the surface geological structure and that the rift zone is deep as 3–9 km (1.9–5.6 mi) locally. The earthquake distribution has been interpreted to have defined the heat source of the Hengill volcano. Extending to the north-east from the central volcano is a fissure swarm with a number of tindars associated with an asymmetrical graben. Lake Thingvallavatn, occupies the proximal graben, and has at its southern end lava flows from the mountain and has hosted explosive eruptions historically. Amongst the faults on the north-west side of the graben is the Almannagjá chasm which extends from the northern shore of Lake Thingvallavatn. Towards the south-east from the mountain towards the sea is a lava covered plateau whose height is about 300–400 m (980–1,310 ft) with scattered higher tindars and tuyas. During the Holocene volcanic eruptions in the zone have been predominantly effusive and basaltic with minor tephra production. Erupted lava volumes have ranged from 0.05–3 km3 (0.012–0.720 cu mi).

Risk The official view of the volcanic hazard is that it is confined to a radius of 30 km (19 mi) and is related to lava flows, plugging of geothermal boreholes by lava, volcano-tectonic faulting and volcanic gas pollution.

There was either hydrothermal fluid or magma increase at a depth of approximately 5–7 km (3.1–4.3 mi) within the inferred brittle-ductile transition zone of the area centred at Ölkelduháls, between Hengill and Hrómundartindur to its east during 2017 and 2018. This volume had been contracting between 2006–2017, and was about 3 km (1.9 mi) north-west from an area of uplift between 1993 and 1999.

Geothermal resources There are three associated geothermal areas related to the high amount of fissuring in the Hengill volcanic system producing high water subsurface permeability. These areas include Iceland's second largest geothermal field which now is an important source of energy for the south of the country. The three areas are:

Nesjavellir geothermal system, which is captured at the Nesjavellir power station near the western shore of the lake Þingvallavatn Hellisheiði, which has the largest power station in Iceland, Hellisheiði power station, approximately 11 km (6.8 mi) south-west of Nesjavelli. Both stations are operated by Orkuveita Reykjavíkur (Reykjavik Energy). Hveragerdi, whose hydrothermal waters have been used for greenhouse heating. The area with its mountains and hot springs is well suited for hiking and there are a lot of hiking trails. The town of Hveragerði with its multitude of hot springs is also part of the Hengill area.

Culture Some folk tales are connected to the region. For example, in a folk tale collected and published by Jón Árnason in 1862, a young farmer is said to have killed the sleeping troll woman Jóra [ˈjouːra] while she lay in wait for innocent wanderers or horsemen on the trail over Dyrafjöll [ˈtɪːraˌfjœtl̥] north of Hengill. In another folk tale, according to some people, a woman's body found in the area was believed to be that of Halla, the wife of the famous Icelandic outlaw Fjalla-Eyvindur.

See also Geography of Iceland List of lakes of Iceland Volcanism of Iceland List of volcanic eruptions in Iceland List of volcanoes in Iceland

Notes

References

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with Hengill

Start with the simplest possible case. Write down what Hengill claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In earth science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Hengill before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Hengill ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Hengill

In research: Hengill appears in earth science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Hengill in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Hengill is common in secondary-school and first-year university syllabi. It links to neighbouring topics Active volcanoes, Central volcanoes of Iceland, Fissure vents, so understanding it makes those chapters shorter.
In everyday life: Look for Hengill outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Hengill in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Hengill means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Hengill out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Hengill in simple terms?

Why does Hengill matter?

Because it connects several earth science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Hengill?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Hengill.