Exfoliating granite is a

granite Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies un ...

undergoing exfoliation, or onion skin weathering (

desquamation Desquamation occurs when the outermost layer of a tissue, such as the skin, is shed. The term is . Physiologic desquamation Keratinocytes are the predominant cells of the epidermis, the outermost layer of the skin. Living keratinocytes reside in ...

). The external delaminated layers of granite are gradually produced by the cyclic variations of temperature at the surface of the rock in a process also called

spall Spall are fragments of a material that are broken off a larger solid body. It can be produced by a variety of mechanisms, including as a result of projectile impact, corrosion, weathering, cavitation, or excessive rolling pressure (as in a ball ...

ing.

Frost Frost is a thin layer of ice on a solid surface, which forms from water vapor in an above-freezing atmosphere coming in contact with a solid surface whose temperature is below freezing, and resulting in a phase change from water vapor (a g ...

and ice expansion in the joints during the winter accelerate the alteration process while the most unstable loosen external layers are removed by

gravity In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...

assisted by runoff water.

Geology

Homogeneous granitic

pluton In geology, an igneous intrusion (or intrusive body or simply intrusion) is a body of intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth. Intrusions have a wide variety of forms and com ...

s are created in high-pressure environments and slowly solidify beneath the earth's crust. Vertical compression of

overburden In mining, overburden (also called waste or spoil) is the material that lies above an area that lends itself to economical exploitation, such as the rock, soil, and ecosystem that lies above a coal seam or ore body. Overburden is distinct from tai ...

releases through

erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is d ...

, or removal of overlying rocks resulting in unloading.Petersen, James F., Dorthy Sack, and Robert E. Gabler. "Pg. 292." Fundamentals of Physical Geography. 1st ed. Belmont: Brooks/Cole, 2010. 292-93. Print.Lutgens, Frederick K., and Edward J. Tarbuck. "Entire Book." Essentials Of Geology. 9th ed. Upper Saddle River: Pearson Prentice Hall, 2006. 118-19. Print. Other contributors of unloading are

tectonic uplift Tectonic uplift is the geologic uplift of Earth's surface that is attributed to plate tectonics. While isostatic response is important, an increase in the mean elevation of a region can only occur in response to tectonic processes of crustal th ...

glacier retreat The retreat of glaciers since 1850 affects the availability of fresh water for irrigation and domestic use, mountain recreation, animals and plants that depend on glacier-melt, and, in the longer term, the level of the oceans. Deglaciation occur ...

, and

mass wasting Mass wasting, also known as mass movement, is a general term for the movement of rock or soil down slopes under the force of gravity. It differs from other processes of erosion in that the debris transported by mass wasting is not entrained in ...

."Forming Yosemite's Famous Granite Domes." My Yosemite Park. N.p., 19 May 2015. Web. 12 May 2017. . The pressure is relieved when the granite is exposed at the surface, allowing it to expand towards the atmosphere. GeologicalExfoliationOfGraniteRock

On the surface, if the granite is not jointed, or if it has few joints, then the exposed surface usually expands faster than the underlying granite. The surface layer, often a couple hundred feet thick, separates from the underlying granite along an expansion joint to form a shell. As this continues, several concentric shells may form to depths of feet or more. Concentric slabs/shells of rock begin to break loose, onion-like layers subparallel to the exterior called

exfoliating Exfoliation is the removal of dead skin cells and built-up dirt from the skin's surface. The term comes from the Latin word ''exfoliare'' (to strip off leaves). This is a regular practice within the cosmetic industry, both for its outcome of pro ...

, sheet jointing, or

fractures Fracture is the separation of an object or material into two or more pieces under the action of stress. The fracture of a solid usually occurs due to the development of certain displacement discontinuity surfaces within the solid. If a displ ...

. As the granite expands the outer, most shells become susceptible to weathering by water pressure, freeze/thaw cycles, and functioning vegetation is a process called physical weathering. The sheets of granite are large enough to shave off sharp edges on the granite's surface creating a dome shape. The overall activity creates exfoliation domes.

Dangers

Rock Falls

Exfoliating rock can trigger

rockfall A rockfall or rock-fallWhittow, John (1984). ''Dictionary of Physical Geography''. London: Penguin, 1984. . is a quantity/sheets of rock that has fallen freely from a cliff face. The term is also used for collapse of rock from roof or walls of mi ...

.Rockfall triggering by cyclic thermal stressing of exfoliation fractures : Nature Geoscience : Nature Research
accessdate: January 5, 2017 Rock Falls in

Yosemite National Park Yosemite National Park ( ) is an American national park in California, surrounded on the southeast by Sierra National Forest and on the northwest by Stanislaus National Forest. The park is managed by the National Park Service and covers an ...

are common and pose threats to visitors.

United States Geological Survey The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, ...

(USGS) conducted a study over a three-year period monitoring granite cracks within the park's Valley. Data collected by Park Geologist Greg Stock, and USGS civil engineer Brian Collins using deformation and temperature gauges. They concluded that there is an outward expansion with the change in thermal temperature up to an inch. With prolonged movement, the cracks expand over time and create exfoliation.

Infrastructure Failure

Twain Harte Lake
Dam is in

Tuolumne County Tuolumne County (), officially the County of Tuolumne, is a county located in the U.S. state of California. As of the 2020 census, the population was 55,620. The county seat and only incorporated city is Sonora. Tuolumne County comprises th ...

located within the Sierra Nevada Mountain Range. Engineers began construction on the dam in 1928 and placed the structure between two granite domes. In August 2014, the granite developed exfoliating joints and began to leak. The process was captured on video and is one of a couple ever to be caught on film. The lake was completely drained and the cost of reconstruction nine-hundred thousand dollars. In June 2016, the granite rock had to be closed off for a second time because of the continued exfoliation.McCaffrey, Tim. "History." Twain Harte Lake. N.p., 2016. Web. 12 May 2017. .

Historic Discovery

Grove Karl Gilbert Grove Karl Gilbert (May 6, 1843 – May 1, 1918), known by the abbreviated name G. K. Gilbert in academic literature, was an American geologist. Biography Gilbert was born in Rochester, New York and graduated from the University of Rochester. D ...

is considered one of the most influential

geologist A geologist is a scientist who studies the solid, liquid, and gaseous matter that constitutes Earth and other terrestrial planets, as well as the processes that shape them. Geologists usually study geology, earth science, or geophysics, althou ...

s of his generation. He was the only president of the Geographic Society to receive the highest honor for geographic accomplishment;

Hubbard Medal The Hubbard Medal is awarded by the National Geographic Society for distinction in exploration, discovery, and research. The medal is named for Gardiner Greene Hubbard, first National Geographic Society president. It is made of gold and is tr ...

.Hunter, Cathy. "Grove Karl Gilbert, “A Captain Bold”." National Geographic Society. N.p., 13 Jan. 2016. Web. 12 May 2017. . Working his way down the

Great Basin The Great Basin is the largest area of contiguous endorheic watersheds, those with no outlets, in North America. It spans nearly all of Nevada, much of Utah, and portions of California, Idaho, Oregon, Wyoming, and Baja California. It is noted fo ...

, Gilbert knew the general formation of mountains through a

tectonic Tectonics (; ) are the processes that control the structure and properties of the Earth's crust and its evolution through time. These include the processes of mountain building, the growth and behavior of the strong, old cores of continents ...

process, and are composed of different rock types. He observed that the mountain ranges in this area contained similarities in

strata In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as e ...

, resembling bubbles and blisters on the earth's surface. He concluded that the mountains were once intrusive

magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natura ...

that had and became visible with erosion. Gilbert presented his findings in a report and contributed significantly in what future generations would know as Geomorphology.

Examples

* Cannon Mountain in the White Mountains of New Hampshire * Enchanted Rock in Texas *

Half Dome Half Dome is a granite dome at the eastern end of Yosemite Valley in Yosemite National Park, California. It is a well-known rock formation in the park, named for its distinct shape. One side is a sheer face while the other three sides are smo ...

, also in Yosemite * Royal Arch in

Characteristics of Exfoliating Granite

* Discontinuity (geotechnical engineering) *

Erosion surface In geology and geomorphology, an erosion surface is a surface of rock (geology), rock or regolith that was formed by erosion and not by construction (e.g. lava flows, sediment deposition) nor fault (geology), fault displacement. Erosional surfaces ...

Foliation (geology) Foliation in geology refers to repetitive layering in metamorphic rocks.Marshak, Stephen, ''Essentials of Geology,'' W. W. Norton 3rd Ed, 2009 Each layer can be as thin as a sheet of paper, or over a meter in thickness. The word comes from th ...

* Geography of the Yosemite area *

Granite dome Granite domes are domical hills composed of granite with bare rock exposed over most of the surface. Generally, domical features such as these are known as bornhardts. Bornhardts can form in any type of plutonic rock but are typically composed o ...

Joint (geology) A rock in Abisko fractured along existing joints possibly by mechanical frost weathering A joint is a break (fracture) of natural origin in a layer or body of rock that lacks visible or measurable movement parallel to the surface (plan ...

Spall Spall are fragments of a material that are broken off a larger solid body. It can be produced by a variety of mechanisms, including as a result of projectile impact, corrosion, weathering, cavitation, or excessive rolling pressure (as in a ball ...

* Spheroidal weathering *

Chemical weathering Weathering is the deterioration of rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs ''in situ'' (on site, with little or no movement ...

occurs in granite exfoliation by changing the mineral composition.Frank, Dave. USGS Geology and Geophysics. N.p., 25 Apr. 2017. Web. 12 May 2017. . * Mechanical Weathering is the breakdown of rocks into smaller fragments or pieces.

References

{{Reflist

External links and references

A nice photo

Exfoliating granite spires, Granite Mts, May 2007 Exfoliating granite spires, Granite Mountains

Exfoliating granite, Mount Kinabalu, Sabah, Borneo

One photo, from the Sierra Nevada

One explanation on Youtube

Another Youtube
* Petersen, James F., Dorthy Sack, and Robert E. Gabler. "Pg. 292." ''Fundamentals of Physical Geography''. 1st ed. Belmont: Brooks/Cole, 2010. 292–93. Print.