Emerging boulder Earthcache (Ward Beach)
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When walking along Ward Beach foreshore towards Chancet Rocks recently I came across some interesting features and, having seen similar features elsewhere in New Zealand, decided to share what might be the birthplace of other (more) famous boulders. A kindergarten here, and off to Moeraki for adulthood perhaps?
A council designated beach walk along mostly flat beach. Any tide for access though low tide is best for Earthcache observations. Allow around an hour return from car parking area.
Appearance.
Concretions vary in shape, hardness and size, ranging from objects that require a magnifying lens to be clearly visible to huge bodies three meters in diameter and weighing several thousand pounds. The giant, red concretions in Theodore Roosevelt National Park, in North Dakota, are almost 3 m (9.8 ft) in diameter. Spheroidal concretions, as large as 9 m (30 ft) in diameter, have been found eroding out of the Qasr El Sagha Formation within the Faiyum depression of Egypt. Concretions are usually similar in color to the rock in which they are found. Concretions occur in a wide variety of shapes, including spheres, disks, tubes, and grape-like or soap bubble-like aggregates.
Composition
They are commonly composed of a carbonate mineral such as calcite; an amorphous or microcrystalline form of silica such as chert , flint, or jasper; or an iron oxide or hydroxide such as geothite and hematite. They can also be composed of other minerals that include dolomite, ankerite, siderite, pyrite, marcasite, barite and gypsum.
Although concretions often consist of a single dominant mineral, other minerals can be present depending on the environmental conditions which created them. For example, carbonate concretions, which form in response to the reduction of sulfates by bacteria, often contain minor percentages of pyrite. Other concretions, which formed as a result of microbial sulfate reduction, consist of a mixture of calcite, barite, and pyrite.
Occurrence
Concretions are found in a variety of rocks, but are particularly common in shales, siltstones, and sandstones. They often outwardly resemble fossils or rocks that look as if they do not belong to the stratum in which they were found. Occasionally, concretions contain a fossil, either as its nucleus or as a component that was incorporated during its growth but concretions are not fossils themselves. They appear in nodular patches, concentrated along bedding planes, protruding from weathered cliffsides, randomly distributed over mudhills or perched on soft pedestals.
Small hematite concretions, dubbed "blueberries" due to their resemblance to blueberries in a muffin, have been observed by the Opportunity rover in the Eagle Crater on Mars.
Cannonball concretions
Cannonball concretions are large spherical concretions, which resemble cannonballs. These are found along the Cannonball River within Morton and Sioux Counties, North Dakota, and can reach 3 m (9.8 ft) in diameter. They were created by early cementation of sand and silt by calcite. Similar cannonball concretions, which are as much as 4 to 6 m (13 to 20 ft) in diameter, are found associated with sandstone outcrops of the Frontier Formation in northeast Utah and central Wyoming. They formed by the early cementation of sand by calcite. Somewhat weathered and eroded giant cannonball concretions, as large as 6 meters (20 feet) in diameter, occur in abundance at "Rock City" in Ottawa County, Kanas. Large and spherical boulders are also found along Koekohe beach near Moeraki on the East coast of the South Island of New Zealand. The Moeraki Boulders and Koutu Boulders of New Zealand are examples of septarian concretions, which are also cannonball concretions.
Large spherical rocks, which are found on the shore of Lake Huron near Kettle Point, Ontario, and locally known as "kettles", are typical cannonball concretions. Cannonball concretions have also been reported from Canada, Greenland, Bosnia-Herzegovina and in Alaska. Reports of cannonball concretions have also come from Hunan Province, China.
Source: Wikipedia; abridged and edited concretions article.
To log this Earthcache please send me your answers to the following questions;
1. What type of rock is prevalent at the site of these boulders?
2. What is the diameter of the boulder attached at WP01?
3. How many boulders form the group at WP02?
4. How long, in time, do you think it will take the boulder slowly emerging at WP03 to become fully detached from the surrounding rock? In your opinion what factors will likely hasten the release of the boulder?
5. What was the condition of the sea near GZ today? Flat calm, massive swells, other?
Optional. Post a photo of any concretion, excluding any that have questions pertaining to them.
You may log your find as once you've sent your answers, I will get in touch if required. Please do not post spoiler photos or answers in your Found It log.
Hope you enjoy your visit to this beautiful place.
Additional Hints
(Decrypt)
Rnegupnpur