This EarthCache focusses on two meteorite impact structures collectively known as the Mahsuri Rings.
Type of Earthcache: Astrobleme / Impact structure.
The Mahsuri Rings
The Mahsuri Rings, two craters formed by the impact of meteorites, were named after Mahsuri, a beautiful maiden who lived in Langkawi during the late 18th century. Wrongly accused of adultery, Mahsuri was sentenced to death. At her execution, she bled white blood, indicating her purity and innocence, while Mahsuri put a curse on the well-being of Langkawi that would last for seven generations. Soon after hear death Langkawi was invaded and languished as a backwater until only recently when the spell expired. Mahsuri's tomb, located at the intersection of the Mahsuri Rings, has become a tourist attraction, it can be found 1.2 kilometres west from the given coordinates1.
Each of the partially superimposed rings is roughly 2.4 kilometres across, with centres at 0.6 kilometres distance apart in 280°-110° direction, and depths of 107 metres for the eastern ring, and 45 metres for the western ring2. The partially encircling rims crest at less than 150 m elevation and are the largest of five confirmed impact structures spread over the Langkawi archipelago.
From the remaining impact structures, two are collectively known as the Malut Rings (previously known as Temoyong Rings), with a fifth referred to as the Tepor Ring, after Pulau Tepor, the nearby horseshoe-shaped islet it struck (or possibly created). The decrease of the diameter of the Malut Rings (both circa 800 metres) and the Tepor Ring (circa 500 metres) in the same direction, suggests that all five impact craters are believed to have been created simultaniously, when a single meteoroid broke up into several meteorites upon entering the atmosphere, resulting a serial impact event.
The impact age of the Langkawi structures is not yet determined. The host rock of the Mahsuri impact structures belongs to the Carboniferous Singa Formation2 and field relations only indicate a post-granite Triassic-Jurassic event3. At the Mahsuri Rings the Singa beds dip into the Triassic-Jurassic Gunung Raya pluton but outward from the ring centres. The ring-like topography of all the four rings of Langkawi are still recognisable. The relatively fast weathering and denudation rates of the humid tropics imply that subaerial exposure of the topography has probably only been since the Neogene. However, the Mahsuri Rings could have been exhumed impact structures, in which case the impact time was at any time since the granite emplacement4.
One distinct feature of an impact crater are materials that have gone through shock-metamorphosis. Shock-metamorphic materials (often rocks) are materials that have been changed because of the impact on the geography around them. This often involves melting or changing the composition of a material; evidence of this is shocked quartz, a shock-metamorphic material found uniquely at impact crater sites on Earth. The supersonic shock waves that emanate from the point of contact of the meteor and Earth's surface create these geologic changes that can allow scientists to identify an impact crater thousands of years after its creation5. In the Langkawi archipelago, three of four arcuate ridges are associated with cleaved quartz that crops out as a sill and dyke complex. Other shock-metamorphic features include ribbon quartz and mosaicism6. No accessible site where shock-metamorphic materials could be observed could be identified for the purpose of this EarthCache.
The Mahsuri Craters as seen from Gunung Raya.
(Source: Langkawi Geopark, 2008. Retrieved January 2019)
From celestial debris to impact structure
The terms comet, asteroid, meteoroid, meteor and meteorite can be confusing. A comet is comparable to an asteroid, with the difference that when they are close enough to the Sun, they display a visible coma (a fuzzy outline or atmosphere due to solar radiation) and sometimes a tail7. An asteroid is a rocky object in space that is smaller than a planet. Sometimes called minor planets or planetoids by NASA, other sources refer to them loosely as space debris or leftover fragments from the formation of the solar system. Meteoroids are a general term describing small particles of comets or asteroids that are in orbit around the sun. There is no universally accepted definition that distinguishes a meteoroid from an asteroid, they are simply smaller than asteroids. A meteor is an asteroid or other object that burns and vaporizes upon entry into the Earth's atmosphere. When a meteor explodes in the atmosphere, the resulting fireball is known as a bolide. When a meteoroid survives a trip through the atmosphere and hits the ground, it's called a meteorite.8. The largest meteorites create impact basins with rings around the edge. Valhalla on Jupiter's moon Callisto is the biggest of these in the Solar System9. No impact basin can be found on Earth.
Impact crater types
On Earth, a meteorite crater, also known as an impact crater, forms when a meteorite greater than 0.9 metres in diameter hits the surface. The size and depth of the crater would depend upon the size and incoming speed of the meteorite. In general, a meteorite that hits Earth's surface creates a crater twelve to twenty times its size10, forming one of two types of craters: simple or complex.
A relatively small meteorite forms a simple impact crater. Measuring typically less than 5 kilometers in diameter, this type of impact crater is relatively smooth, bowl-shaped, and nearly circular. The rim or upper edge of the crater is well-defined and raised above the surrounding landscape. The interior of the crater is steepest near the rim. The slope gradually decreases toward the center of the crater. Partially lining the interior of the crater is a layer of breccia (a coarse-grained rock composed of angular, broken rock fragments held together by a mineral cement). The energy of the impact typically causes some rocks to melt. In simple craters, this impact melt is often found as small blobs of material within the breccia layer. Surrounding the rim of the crater is a circular layer of rock and dust thrown out of the crater during its formation. Known as an ejecta blanket, this layer is deepest close to the rim. It becomes increasingly shallow outward from the crater11.
Cross section of a typical simple crater.
A larger meteorite forms a complex impact crater, which generally measures more than 3 kilometres in diameter. While the interior of a complex crater may initially be smooth, it does not remain so for long. Gravity causes the steep walls to collapse downward and inward, forming terraced walls that may produce additional rims or rings within the crater. In the center of a complex crater lies a distinct central peak. The peak forms as the crater floor rebounds from the shock of the meteorite impact. The largest complex impact craters have several rings and several inner peaks. Breccia also partially fills complex craters, and its layer may contain sheets of impact melt. An ejecta blanket surrounds a complex impact crater much as it does a simple impact crater12.
Cross section of a typical complex crater.
Legend.
An impactor does not create a hole by pushing aside material to form an impact crater. What really happens is an explosion! Even small craters are created by very energetic events. Impactors that plow into Earth are moving extremely fast, anywhere from 15 to 70 kilometres per second! Compare that to the speed of a bullet, which travels between 335 and 427 metres per second! All that speed means a lot of momentum, and a lot of energy. That energy gets transferred right into the ground, making dramatic changes to the rocks, the most noticeable of which is the huge explosion that creates the impact crater itself. Because of the energies involved, it doesn't take a very big impactor to create a big crater13.
That energy is what drives the creation of the impact crater. For simplicity, we can split the formation of a crater into 3 stages: contact and compression, excavation, and modification. During the first stage, the energy forces the target rocks down and compresses them. A transient crater starts to form, "transient" as this early crater will change. Material is then melted, even vaporized, and starts to be thrown out of the rapidly expanding crater during the excavation stage. For relatively small impact events the transient crater is relatively stable and we end up with a simple crater. For larger impact events, however, this transient crater is unstable, it's basically too deep and wide. Rocks at the bottom of these craters resist being compressed and deformed, and eventually 'snaps back' during the modification stage. This is the process that pushes up the central peak in complex craters. Finally, the ejecta falls to the ground, and the rim and center of the crater slump a bit and settle into their final shapes. All of this happens within a few minutes, although for larger craters the melted rocks can take a very long time to cool and harden again, and the rim and peaks may fall and slump a bit more. Every impact structure changes with time, given what is going on around them in their environment. On the Moon, where there is no wind, rain, or atmosphere to speak of, craters can remain fresh-looking for quite a while14. On the Earth, however, which has been even more heavily impacted than the Moon, craters are continually erased by erosion and redeposition as well as by volcanic resurfacing and tectonic activity15.
As is the case with most impact craters on Earth, the craters on Langkawi are not easily recognized due to weathering and erosion. In fact, they are barely known even among the local populace, and most would come and go without even realising they've passed through not one, but two ancient impact craters! Material from the weathered down crater rims have undoubtedly contributed much of the alluvium deposit that fill the craters today. Such alluvium deposits often result in very fertile soils as, coincidentally, can be witnessed on location in the form of flat paddy land.
Interesting facts
- Over 40 large arcuate to circular patterns have been identified in Peninsular Malaysia. Gravity and magnetic anomalies might reveal as of yet undiscovered impact structures in the future. Even in Langkawi, various out of place breccia sites, some researched in previous decades and now largely overgrown and inaccessible, suggest the existence of several other impact sites, heavily obscured from view due to natural weathering, human activity and the fact that they might be partially or completely submerged.
- The phenomena of a meteor burning up in the atmosphere is commonly known as a "shooting star". It is considered a symbol of good luck, magic, dreams and wishes across the globe.
- Excluding major showers, like the annual Perseids shower mid-June or the Geminid shower around December, sporadic meteors streak across the sky at a rate of 2 to 16 per hour, year round. If you pay attention, it is essentially unavoidable that you will see one eventually. If you want to improve your odds, go outside an hour before sunrise. This is when you are on the side of the planet facing in its direction of travel around the sun, and meteors can appear three times as often as after dusk, when you are on the trailing side of Earth. Despite all this activity, the chance of a meteorite landing near or on top of you is extremely low and highly unlikely.
- An estimated 100 to 200 tons (91 to 181 metric tons) of extraterrestrial material bombards Earth's surface every day. Much of this material ranges in size from dust to pebbles and lands unnoticed. During the planet's history, though, thousands of impacts have produced craters, some of which have measured 160 kilometres or more in diameter.
- The Moon is thought to be a planetoid that crashed into Earth 4.5 billion years ago. The giant-impact hypothesis, sometimes called the Big Splash or the Theia Impact, suggests that the Moon formed out of the debris left over from a collision between Earth and an astronomical body the size of Mars, approximately 4.5 billion years ago, in the Hadean eon; about 20 to 100 million years after the Solar System coalesced. That "giant impactor", Theia, who in Greek mythology was mother to the goddess of the moon, is thought to have been roughly the size of Mars and to have been pulverized in the encounter, along with a good chunk of proto-Earth. From that fiery cloud of all-Theia and part-Earth, the scenario goes, our moon soon condensed16. Theia's isotopic thumbprint has been confirmed from an aspirin's worth of pure Apollo rock (rocks brought back from the moon during the Apollo missions between 1966 and 1972), so this hypothesis is not without merit.
- Chicxulub on the Yucatan coast in Mexico is considered by most scientists as the source crater of the catastrophe that led to the extinction of the dinosaurs at the end of the Cretaceous period. Another interesting fact about the Chicxulub crater is that you cannot see it. Its circular structure is nearly a kilometer below the surface and was originally identified from magnetic and gravity data15. Initially, the crater measured nearly 100 kilometres in diameter and 14 kilometres in depth. The energy released by the impact was 6 million times more powerful than that released during the 1980 eruption of Mount St. Helens in Washington state. The walls of the complex impact crater were unstable and soon collapsed inward. The final diameter of the crater was enlarged to between 145 and 180 kilometres. During the crater's formation, clouds of water vapor and debris were thrown into the sky. Some of the 100 billion tons (91 billion metric tons) of vaporized material solidified into glassy spheres and rained back down on Earth. The rest of the material rose into the atmosphere where winds carried it around the planet. The material blocked sunlight from reaching Earth's surface, reducing temperatures worldwide17.
Depiction of the extinction of the dinosaurs.
How to claim this EarthCache?
Send me the following;
1. The text "GC81GQ0 The Mahsuri Rings" on the first line.
2. The answers to the following questions;
- The hills nearest to you are in fact crater rims. Estimate their maximum height.
- Can you determine if you are standing in crater 1, 2 or both? Explain.
- From which direction would the meteor have struck the island? Explain.
- Why is there no typical impact crater visible? Provide two reasons.
- Provide the average diameter of the meteorites that caused these craters.
- Would you classify the Mahsuri Rings as simple or complex craters? Why?
- What is the name of the most famous crater ever caused by a meteor?
- What is the number on the pole nearest the coordinates?
3. Provide a photo of yourself or a personal item to prove you have visited the site.*
References
* Effective immediately from 10 June 2019, photo requirements are permitted on EarthCaches. This task is not optional, it is an addition to existing logging tasks! Logs that do not meet all requirements posed will no longer be accepted.
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1 Shock structures in Peninsular Malaysia: evidence from Kedah and Pahang, H. D. Tjia & Mazlan Mahamad Zain, Bulletin of the Geological Society of Malaysia, volume 45, May 2002, p. 104. 2 Warta Geologi, newsletter of the Geological Society of Malaysia, volume 28, No.3, May 2002, p 110-111. 3 Shock structures in Peninsular Malaysia: evidence from Kedah and Pahang, H. D. Tjia & Mazlan Mahamad Zain, Bulletin of the Geological Society of Malaysia, volume 45, May 2002, p. 104. 4 Shock structures in Peninsular Malaysia: evidence from Kedah and Pahang, H. D. Tjia & Mazlan Mahamad Zain, Bulletin of the Geological Society of Malaysia, volume 45, May 2002, p. 107. 5 GeoLounge, Impact Craters, Elizabeth Borneman, September 2014, retrieved January 2019. 6 Hydrocarbon potential of meteorite impact structures, Focus on Sundaland, H. D. Tjia, Jakarta, January 2004. 7 What are an asteroid, a meteor and a meteorite? (adaptation by cache owner), Marc Lallanilla, LiveScience, 2013. 8 Meteors and meteorites, NASA, January 2019, retrieved February 2019. 9 Crater types, How It Works, March 2013, retrieved February 2019. 10, 11, 12 Meteorite crater, Science Clarified, undated, retrieved January 2019. 13 Explorer's guide to impact craters (adaptation by cache owner), Planetary Science Institute, undated, retrieved February 2019. 14 Revisiting the Moon, The New York Times, September 2014. 15 Terrestrial Impact Craters, Koeberl, Christian and Virgil L. Sharpton, undated (1986 / 1990?), retrieved February 2019. 16 Exploring the Moon, NASA EG-1997-10-116-HQ. 17 Meteorite crater, Science Clarified, undated, retrieved January 2019.
