As stated in the introduction to Jiaming Lake above, there are two theories that surround how this lake was formed — The Meteorite Theory and the Glacial Theory. Your task will be to observe the rocks near the lake to provide geological evidence in support of the theories.
In order to prove which theory is correct based on the evidence provided by the geologists suppoting their respective theories, we will try to understand the geological difference between Meteorites and Glacial Moraines, and then based on our observations at the lake, determine the origin of Jiaming Lake. Below you will find two parts outlining Meteorites and Glacial Moraines.
Meteorites are often mistakingly called meteors. Meteor is the scientific name for the atmospheric effect caused by a piece of extraterrestrial matter burning in our atmosphere, and should not be confused with the word meteorite, which refers to any material that actually lands. A bright and typically very short-lived meteor is caused by atmospheric drag and friction acting on an incoming body that becomes so hot it literally incandesces, as does the air around it. Most meteors glow for only a few seconds or less, and that brief period of intense heat is part of what makes any surviving meteorites so very unique and fascinating. The extremely high temperatures cause surfaces to melt and flow, creating remarkable features that are entirely unique to meteorites such as regmaglypts, fusion crust, orientation, and rollover lips (more on these features below).
SOME BASIC FACTS ABOUT METEORITES
Are meteorites are attracted to magnets?
Nearly all meteorites contain a significant amount of extraterrestrial iron, even those that look similar to terrestrial rocks (stony meteorites). Test your find with a good hardware store magnet or our rare earth magnet. An extremely small percentage of meteorites do not show strong attraction to a magnet. Those meteorites look similar to volcanic rocks from Earth, and are not metallic in appearance.
Rare Earth Magnet Photo 2
Most meteorites will adhere strongly to a good magnet
Are meteorites heavy?
Most meteorites are much denser than ordinary Earth rocks. The thing most people say when they hold a meteorite for the first time is, “Wow! It’s so heavy!” The unusual weight is due to high iron content.
Are meteorites radioactive?
Meteorites likely traveled in space for millions of years before visiting us here on Earth. They were bathed in cosmic rays, but are not dangerous or radioactive.
WHAT DOES A METEORITE LOOK LIKE?
Please see helpful pictures of meteorites below
An iron meteorite (Canyon Diablo) from Arizona’s Meteor Crater. Note orange patina and adhesion of strong magnet
OLD STONE METEORITE
A moderately weathered stone meteorite (NWA 869) found in the Sahara Desert. Note adhesion of strong magnet
FRESH STONE METEORITE
A stone meteorite (Gao-Guenie) which fell in Africa in 1960. Note the rich black fusion crust and the large surface dimples
CHARACTERISTICS OF METEORITES
Attraction to a magnet
Meteorites are dense, they will feel heavier than ordinary Earth rocks of a similar size.
Recently fallen meteorites will have fusion crust on the outside. This is a thin black rind, sometimes shiny, sometimes matte black, which forms while falling meteoroids are super-heated in the atmosphere.
Meteorites, especially irons, often acquire “regmaglypts” (thumbprints) caused when their surface melts during flight. Stone meteorites sometimes display regmaglypts too, but they are typically not as well defined as in irons.
An iron meteorite which fell in Russia in 1947. It displays many fine regmaglypts. This is what a freshly-fallen iron meteorite would look like
An older iron meteorite in as-found condition. This meteorite has been on Earth for centuries. Note the surface features (regmaglypts) and rust
An iron meteorite found in the Namibian desert. This meteorite has been on Earth for centuries. Note the angular shape, large regmaglypts and desert patina
Nearly all stone meteorites contain small, bright metallic flakes. These are tiny pieces of extra-terrestrial iron and nickel. You can usually see them after slicing off a small piece, or removing a corner with a bench grinder.
Chondrules are small, colorful, grain-like spheres which occur in most stone meteorites, hence the name chondrites. Chondrites are the most abundant type of meteorite and chondrules are not found in earth rocks.
Rust or patina
We often are asked, “Do meteorites rust?” Meteorites that have been on the Earth for a long time will likely start to rust, or — in dry desert environments — acquire a patina caused by oxidation. The natural patina of irons is often yellow/ochre, red, or orange.
Most potential meteorites spin and tumble as they plummet through the atmosphere. Occasionally, one will maintain a fixed orientation towards the surface of our planet, causing the leading edge to ablate into a shield, nose cone, or bullet shape. When meteorites ablate, some of their mass is removed as a result of vaporization. Meteorites which display such features are quite rare and are described as oriented.
Most stone meteorites contain abundant small metallic flakes composed of nickel and iron. These flakes cause stone meteorites to feel heavy
Most stone meteorites contain grain-like components known as chondrules. Chondrites (containing chondrules) are the most common type of meteorite
Flowlines (caused by melting) and glossy fusion crust on an Australian Millbillillie stone meteorite — one of the very few that will not stick to a magnet
隕石經常被誤稱為流星。流星是大氣現象的科學專有名詞，這種大氣現象是由一塊外星物質在大氣中燃燒所造成，跟會實際落在地表的隕石並不相同，明亮且存在時間短暫的流星由外來物與大氣摩擦產生高熱、產生白熾光，大部分流星只存在幾秒鐘或更短，這個短暫的高熱讓所有存留下來的隕石都更為特殊、吸引人。極端高溫讓隕石表面融化、流動，造成標誌性的特徵，幾乎是專屬於隕石的特徵，像是氣印(regmaglypts)、熔殼(fusion crust)、定向(orientation)、卷邊(rollover lips)等。
Moraines are distinct ridges or mounds of debris that are laid down directly by a glacier or pushed up by it1. The term moraine is used to describe a wide variety of landforms created by the dumping, pushing, and squeezing of loose rock material, as well as the melting of glacial ice.
Moraine ridges on the forefield of the Matanuska Glacier, Alaska. Photo: Frank K.
In terms of size and shape, moraines are extremely varied. They range from low-relief ridges of ~1 m high and ~1 m wide formed at the snout of actively retreating valley glaciers2, to vast ‘till plains’ left behind by former continental ice sheets3.
Low-relief moraine ridges on the forefield of the actively retreating Skaftafellsjökull Glacier in Iceland. The moraines mark former ice extent and mirror the shape of the glacier terminus at the time of formation. Photo: TommyBee
Moraines consist of loose sediment and rock debris deposited by glacier ice, known as till. They may also contain slope, fluvial, lake and marine sediments if such material is present at the glacier margin, where it may be incorporated into glacial ice during a glacier advance, or deformed by glacier movement4,5.
Moraine composed of loose rock and sediment forming at the lateral margin of the Boulder Glacier, Washington, USA. Photo: W. Siegmund.
Moraines are important features for understanding past environments. Terminal moraines, for example, mark the maximum extent of a glacier advance (see diagram below) and are used by glaciologists to reconstruct the former size of glaciers and ice sheets that have now shrunk or disappeared entirely6.
Summary of the main moraine types and their spatial patterns. The top diagram is a cross-section through a cirque glacier. The bottom diagram is drawn in plan view, looking down on the surface of a valley glacier made up of several tributaries. Image created by J. Bendle.
The most common moraine types are defined below:
A terminal moraine is a moraine ridge that marks the maximum limit of a glacier advance. They form at the glacier terminus and mirror the shape of the ice margin at the time of deposition. The largest terminal moraines are formed by major continental ice sheets and can be over 100 m in height and 10s of kilometres long7,8.
Terminal moraine marking the limit of the former Patagonian Ice Sheet at the Last Glacial Maximum (~25 to 18 thousand years ago). Photo: J. Bendle.
Recessional moraines are found behind a terminal moraine limit and form during short-lived phases of glacier advance or stillstand that interrupt a general pattern of glacier retreat. In some cases, recessional moraines form on a yearly basis (normally as a result of winter glacier advances) and are known as annual moraines9,10,11.
Recessional moraines (arrowed) marking the shrinkage of a South American valley glacier. The glacier (not shown) retreated towards the south-west, leaving behind a moraine-dammed glacial lake. Imagery from GoogleEarth, diagram created by J. Bendle.
Lateral moraines form along the glacier side and consist of debris that falls or slumps from the valley wall or flows directly from the glacier surface12 (see image below). Where the rate of debris supply is high, lateral moraines can reach heights of more than 100 metres12–15.
Lateral moraine of the Callequeo Glacier of the San Lorenzo Icefield in central Patagonia, South America. Photo: J. Martin.
The term latero-frontal moraine is used where debris builds up around the entire glacier tongue14. These moraine types are common in mountain settings such as the European Alps, the Southern Alps of New Zeland (see the Mueller Glacier moraines below) and the Himalayas, where the high supply of rock debris from unstable valley sides, rapidly build up at the glacier margins.
Latero-frontal moraine complex of the Mueller Glacier, South Island, New Zealand. The debris-covered and downwasting Mueller Glacier is flanked by lateral moraines of ~100 m in height, which continue down valley and merge into terminal moraines. Imagery from GoogleEarth, diagram created by J. Bendle.
Medial moraines are debris ridges at the glacier surface running parallel to the direction of ice flow4,5. They are the surface (or supraglacial) expression of debris contained within the ice. Medial moraines form where lateral moraines meet at the confluence of two valley glaciers, or where debris contained in the ice is exposed at the surface due to melting in the ablation zone16.
Medial moraines on the surface of an Alaskan valley glacier. In this example, surface debris is concentrated at the point where two glaciers merge. Imagery from GoogleEarth, diagram created by J. Bendle.
Ground moraine is a term used to describe the uneven blanket of till deposited in the low-relief areas between more prominent moraine ridges6. This type of moraine, which is also commonly referred to as a till plain, form at the glacier sole as due to the deformation and eventual deposition of the substratum.
冰磧物是指冰川融化以後遺留在地面上的大小石塊或黏土(歐洲)的堆積物，這些堆積物可以造成小山丘或其他地形。有許多不同種類的冰磧，冰川活動切割地景來形成這些冰磧。側磧(lateral moraines)成形於冰川側邊，表磧(supraglacial moraines)成形於冰川上方，中磧(medial moraines)成形於冰川中間，終磧(terminal moraines)則是成形於冰川尾端。
In order to log a Found It! on this Earth Cache, please send me the answers to the following Task Questions:
Based on what you have learned from above about characteristics of Meteorites, take a walk around Jiaming Lake and observe the rocks. Describe their appearance. Also, pick up some of the rocks and compare their weight. Are rocks of similar size and shape the same weight or are some heavier than others? Lastly, use a strong magnet to test if these rocks have any magnetic charge to them.
Based on what you have learned from above about Glacial Moraines, take a walk around Jiaming Lake and observe any characteristics present that would indicate the former presence of a glacier here. Based on what you observe, what defining characteristics, if any, can you see of Glacial Moraines?
Based on your observations on the on-site tasks you completed, which theory is more likely to prove how Jiaming Lake formed? What factors do you think cause the debate over how this lake was formed?
Optional — Post of picture of you with your GPS at Jiaming Lake
You may log your find as soon as you send me your answers, but you must visit the site and complete the tasks. Please uphold the integrity of this game and do not log this cache unless you actually visit this Earth Cache. I hope you enjoy your visit to Jiaming Lake!