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Maar Volcano - Lunar Crater

A cache by DK_Titan Send Message to Owner Message this owner
Hidden : 09/13/2012
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Geocache Description:

Please be aware that this is an Earthcache, which requires you to answer the questions in the assignment mentioned in the cache description. Please send these answers via our profile on Feel free to contact us if you have questions regarding the assignment or any other comments to the cache.

Maar Volcano - Lunar Crater

Lunar Crater seen from North

The Lunar Crater Volcanic Field is located in a very deserted area in central Nevada. The nearest towns are Tonopah (84 miles) and Ely (97 miles) so bring plenty of water and gas, and don't expect cell phone coverage out here!

Map of the Lunar Crater Volcanic Field (reproduced from Valentine GA et al. (see below))

At Waypoint 1 (the cache coordinates) you will be overlooking the Lunar Crater, which has the typical shape of a maar volcano. From this location you will also see another volcano towards north northeast (approx. 26°) which has a very different appearance. Please describe in your own words the shapes of these two volcanos and try to explain why they differ.

You should now head for Waypoint 2 (N 38° 23.281 W 116° 04.109) which is a reference point that will lead you to Waypoint 3 (N 38° 23.278 W 116° 04.119). At Waypoint 3 you will be right below a steep rock wall towards north. Enjoy the great view of the crater from here! Please describe this rock wall (structure, color, texture).

As mentioned in the cache description below, a group of researchers lead by Dr. Greg A. Valentine recently visited the Lunar Crater. According to their research, is the size of this maar the result of a series of explosions (incremental growth) or is it due to one large explosion?

Optional: We also very much appreciate you uploading a photo with your log (preferably of you or someone from your team with the beautiful crater in the background), but this is not a log requirement.

Lunar Crater seen from a bit below the rim

About the volcano:
Lunar Crater is not the result of a meteor impact, but is a so-called maar, which was created by highly energetic volcanic eruptions. The word "maar" comes from the German word, which is derived from the Latin word "mare" (sea). Maar volcanoes are formed when lava or magma come into contact with groundwater. This causes an enormous explosion which is the reason for the shape of this type of volcanoes. They are broad, low-relief craters, which are often filled with water, forming a crater lake. However, at this location the groundwater is too far below the surface to form a lake in the Lunar Crater. The crater measures almost 4000 feet across and is 430 feet deep.

Cross-section of Citadel Mountain and Lunar Crater (reproduced from Valentine GA et al. (see below))

The resemblance between a maar and a meteor crater is striking, and this is probably the reason why this place was used to train astronauts for the Apollo moon missions in the late 1960s.

Recently researchers from the University of Buffalo, New York focused on Lunar Crater in a scientific article trying to explain the shape and size of maar craters. (See link to the article below). Two different models are proposed, which might explain the dimensions and depth of the crater: The incremental growth model, which suggests that the crater is formed by the integrated result of many explosions and the major-explosion dominated model, which states, that the size of the crater is determined by the largest single explosion during the lifetime of the maar.

Based on the geological evidence found here at Lunar Crater, the authors conclude that incremental growth model seems most appropriate for this particular maar. Furthermore, they find it likely that the same conclusion would be reached for most other maar volcanoes.

Not all volcanoes in the Lunar Crater Volcanic Field are of the maar type. The area also offers the opportunity to see cinder cones and according to some sources a so-called collapsed cinder cone. A cinder cone is a steep conical hill consisting of volcanic debris that accumulates around and downwind from a volcanic vent. In comparison to a maar eruption, the eruption forming a cinder cone (called a "Strombolian eruption") is much less energetic. However, the eruption of a cinder cone can be much more long-lasting. One example is the cinder cone on the Italian island of Stromboli, which has been erupting almost continuously for the past 2000 years!

Shetch of a cinder cone (reproduced from ref 4)

1. Maar - Wikipedia article
This Wikipedia article explains the formation of maar volcanoes and mentions a number of different examples of maars from around the World. It also includes a gallery of photos of such volcanos.

2. America's Byways - Lunar Crater Volcanic Field
This web page gives a short description of the Lunar Crater Volcanic Field and mentions the use of this area for training of astronauts for the Apollo moon missions.

3. Valentine GA et al. (2011) Models of maar volcanoes, Lunar Crater (Nevada, USA). Bull Volcanol 73: 753-765
Abstract of this scientific article:
Maar volcanoes are generally understood to be the result of highly energetic, explosive interaction between magma and water (groundwater or surface water). Two end-member conceptual models have been proposed to explain the dimensions (diameter, depth) of maar craters: (1) an incremental growth model, where a crater grows due to subsidence and ejection of debris over the course of many explosions, and the final size is an integrated result of multiple explosive events; (2) a model in which the dimensions of a maar crater are the result of the largest single explosion during the lifetime of the maar (major-explosion dominated model). In the latter case, the maar size can be used to estimate the energy and depth of the largest explosion, which in turn allows estimation of the magma mass involved. This paper describes Lunar Crater maar (Nevada, USA) and tests the two models as explanations for the characteristics of the volcano, in particular the major-explosion dominated model. This model implies magma mass and supply rates that are unrealistic, and the tephra at the maar do not contain key features observed in the ejecta at large single-explosion craters. The incremental growth model seems most suitable based upon geological evidence.

4. The three main types of volcanoes
This web page gives a good description of different types of volcanoes (including cinder cones)

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