earth science

Maar

Maar 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 Maar rather than just read about it. In short: A maar is a broad, low-relief volcanic crater caused by a phreatomagmatic eruption (an explosion which occurs when groundwater comes into contact with hot lava or magma). A maar characteristically fills with water to form a relatively shallow crater lake, which may also be called a maar.

Key takeaways

Maar 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 Maar to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Maar from memory before moving on to harder problems.

Reference excerpt

A maar is a broad, low-relief volcanic crater caused by a phreatomagmatic eruption (an explosion which occurs when groundwater comes into contact with hot lava or magma). A maar characteristically fills with water to form a relatively shallow crater lake, which may also be called a maar. Maars generally range in size from 20 to 3,000 m (66 to 9,800 ft) across and from 5 to 200 m (20 to 700 ft) deep. Most maars fill with water to form natural lakes. Most maars have low rims composed of a mixture of loose fragments of volcanic rocks and rocks torn from the walls of the diatreme.

Etymology The name maar comes from a Moselle Franconian dialect word used for the circular lakes of the Daun area of Germany. The word evolved from its first use in German in the modern geological sense in 1819 and is now used in English and in the geological sciences as the term for the explosion crater, even if water from rainfall might always have drained from the crater after the formation event. This extension in meaning was due to recognising that the lake may no longer exist. Since maar lakes are formed after initially ground or subsurface water interacts with a magma intrusion to create an explosion crater, the name came to be used for the crater type as well. The present definition of the term relates to both its common and scientific discourse use in language over two centuries. Depending upon context there may be other descriptors available to use in the geological sciences such as the term tuff ring or maar-diatreme volcanoes. These last are volcanoes produced by explosive eruptions that cut deeply into the country rock with the maar being "the crater cut into the ground and surrounded by an ejecta ring". A 2011 geological clarification of a maar is "Maar volcanoes are distinguished from other small volcanoes in having craters with their floor lying below the pre-eruptive surface".

Maar lakes and dry maars Maar lakes, also referred to simply as maars, occur when groundwater or precipitation fills the funnel-shaped and usually round hollow of the maar depression formed by volcanic explosions. Examples of these types of maar are the three maars at Daun in the Eifel mountains of Germany. A dry maar results when a maar lake dries out, becomes aggraded or silted up. An example of the latter is the Eckfelder Maar. Near Steffeln is the Eichholzmaar (also called the Gussweiher) which has dried out during the last century and is being renaturalised into a maar. In some cases the underlying rock is so porous that maar lakes are unable to form. After winters of heavy snow and rainfall many dry maars fill partially and temporarily with water; others contain small bogs or often artificial ponds that, however, only occupy part of the hollow.

Distribution The largest known maars are found at Espenberg on the Seward Peninsula in northwest Alaska. These maars range in size from 4 to 8 km (2.5 to 5.0 mi) in diameter and a depth up to 300 m (980 ft). These eruptions occurred in a period of about 100,000 years, with the youngest (the Devil Mountain Maar) occurring about 17,500 years ago. Their large size is due to the explosive reaction that occurs when magma comes into contact with permafrost. Hydromagmatic eruptions are increasingly explosive when the ratio of water to magma is low. Since permafrost melts slowly, it provides a steady source of water to the eruption while keeping the water to magma ratio low. This produces the prolonged, explosive eruptions that created these large maars. Examples of the Seward Peninsula maars include North Killeak Maar, South Killeak Maar, Devil Mountain Maar and Whitefish Maar. Maars occur in western North America, Patagonia in South America, the Eifel region of Germany (where they were originally described), and in other geologically young volcanic regions of Earth. Elsewhere in Europe, La Vestide du Pal, a maar in the Ardèche department of France, is easily visible from the ground or air. Kilbourne Hole and Hunt's Hole, in southern New Mexico near El Paso, Texas, are maars. The Crocodile Lake in Los Baños in the Philippines, though originally thought to be a volcanic crater, is a maar. The carbon dioxide-saturated Lake Nyos in northwestern Cameroon is another example, as is Zuñi Salt Lake in New Mexico, a shallow saline lake that occupies a flat-floored crater about 6,500 ft (2,000 m) across and 400 ft (120 m) deep. Its low rim is composed of loose pieces of basaltic lava and wall rocks (sandstone, shale, limestone) of the underlying diatreme, as well as chunks of ancient crystalline rocks blasted upward from great depths. Maars in Canada are found in the Wells Gray-Clearwater volcanic field of east-central British Columbia and in kimberlite fields throughout Canada. Another field of maars is found in the Pali-Aike Volcanic Field in Patagonia, South America. and in the Sudanese Bayuda Volcanic Field. The Auckland volcanic field in the urban area of Auckland, New Zealand, has several maars, including the readily accessible Lake Pupuke in the North Shore suburb of Takapuna. Arizona's Meteor Crater was for many years thought to be a maar of volcanic origin but it is now known to be an impact crater.

Germany

Eifel maars

In the Volcanic Eifel there are about 75 maars. Both lake-filled and dry maars are typical, though the latter are more common. The last eruptions took place at least 11,000 years ago, and many maars are older, as evidenced by their heavy erosion and less obvious shapes and volcanic features.

Water-filled maars of the Eifel

Dry maars of the Eifel

In the Eifel and Volcanic Eifel there are numerous dry maars:

Mosbrucher Weiher (4 km SE of Kelberg) Booser Doppelmaar (W of Boos; near Kelberg) Dreiser Weiher (W of Dreis-Brück, N of Daun) Dürres Maar (SW of Gillenfeld) Duppacher Weiher (near Duppach, NW of Gerolstein) Geeser Maar (E of Gerolstein, N of Gees) Eckfelder Maar (near Eckfeld) Eigelbacher Maar (near Kopp, county of Daun; maar basin: c. 1200 m × 1200 m) Hitsche Maar (NW of the Dürre Maar, smallest Eifel maar; Ø = 60 m) Immerather Risch (Middle Low German: risch = reed bed; N of the Immerather Maar) Gerolsteiner Maar (NE of Gerolstein) Schalkenmehrener Maar E (of Schalkenmehren) Schönfelder Maar (SW of Stadtkyll-Schönfeld) Steffelner Laach or "Laach Maar" (near Steffeln) Dehner Maar (near Reuth) Walsdorfer Maar ("Schilierwiese"; S of Walsdorf; maar basin: c. 1150 m × 1000 m) Wollmerather Maar (near Wollmerath)

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Maar

Start with the simplest possible case. Write down what Maar 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 Maar 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 Maar 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 Maar

In research: Maar 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 Maar 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: Maar is common in secondary-school and first-year university syllabi. It links to neighbouring topics Depressions (geology), Maars, Volcanic craters, so understanding it makes those chapters shorter.
In everyday life: Look for Maar 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 Maar in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Maar 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 Maar out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Maar in simple terms?

Why does Maar 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 Maar?

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 Maar.