A
serpentine soil is derived from ultramafic rocks, in particular
serpentiniteSerpentinite is a rock composed of one or more serpentine group minerals. Minerals in this group are formed by serpentinization, a hydration and metamorphic transformation of ultramafic rock from the Earth's mantle. The alteration is particularly important at the sea floor at tectonic plate...
, a rock formed by the hydration and
metamorphicMetamorphic rock is the result of the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form". The protolith is subjected to heat and pressure causing profound physical and/or chemical change...
transformation of ultramafic rock from the Earth's
mantleThe mantle is a part of a terrestrial planet or other rocky body large enough to have differentiated by density. The interior of the Earth, similar to the other terrestrial planets, is chemically divided into layers. The mantle is a highly viscous layer between the crust and the outer core...
.
The soils derived from ultramafic bedrock give rise to unusual and sparse associations of
edaphicEdaphic is a general term referring to characteristics of the soil. This could be, for example, the drainage, the texture, or soil chemical properties, such as the pH. Edaphic characteristics are often used to describe plant communities that are found only on specific soil conditions...
(and often endemic) plants that are tolerant of extreme soil conditions, including:
- low calcium:magnesium ratio
- lack of essential nutrients such as nitrogen, potassium, and phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus is commonly found in inorganic phosphate rocks. Elemental phosphorus exists in two major forms – white phosphorus and red phosphorus...
and
- high concentrations of the heavy metals (more common in ultramafic rocks).
These plants are commonly called serpentine endemics, if they grow only on these soils. (Serpentinite is composed of the mineral serpentine, but the two terms are often both used to mean the rock, not its mineral composition.)
As ecologic indicator
Excellent examples of serpentine soils and the distinctive ecologic communities associated with them have been described in western North America.
For instance, in areas where these ultramafic rocks are patchy, such as the
Klamath BasinThe Klamath Basin is the region in the U.S. states of Oregon and California drained by the Klamath River. It contains most of Klamath County and parts of Lake and Jackson counties in Oregon, and parts of Del Norte, Humboldt, Modoc, Siskiyou, and Trinity counties in California. The drainage basin...
region of northern California, the areas of serpentine soil can be clearly seen as sparsely covered areas bounded by forest on the normal soils.
Botany
Areas of serpentine soil are also home to diverse
wildflowerA wildflower is a flower that grows wild, meaning it was not intentionally seeded or planted. Yet "wildflower" meadows of a few mixed species are sold in seed packets. The term "wildflower" has been made vague by commercial seedsmen who are interested in selling more flowers or seeds more...
s, many of which are
rareA rare species are an organism which are very uncommon or scarce. This designation may be applied to either a plant or animal taxon, and may be distinct from the term "endangered" or "threatened species" but not "extinct"....
or
endangered speciesAn endangered species is a population of organisms which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters. Also it could mean that due to deforestation there may be a lack of food and/or water...
such as
Acanthomintha duttoniiAcanthomintha duttonii is a species of annual plant endemic to San Mateo County, California in the Lamiaceae family. It is commonly called San Mateo Thornmint or Dutton's acanthomintha and is found growing on Serpentine soils near the Crystal Springs Reservoir in a six mile long strip on the east...
,
Pentachaeta bellidifloraPentachaeta bellidiflora is a Californian wildflower in the genus Pentachaeta of the family. It is included in both the state and federal lists of endangered species....
, and
Phlox hirsutaYreka phlox is a species of phlox. It is a small flowering plant that grows in the serpentine soils of Siskiyou County, California and is the official city flower of Yreka, California, after which it is named.Yreka phlox plants grow to a height of up to six inches, with thick hairy stems at the...
. In California, shrubs such as leather oak (
Quercus durataQuercus durata is an oak endemic to California. This plant is often used as an urban tree and medicinal plant....
) and coast whiteleaf manzanita (
Arctostaphylos viscida ssp.
pulchella) are typical of serpentine soils.
Appearance
Serpentine-rich rock has a mottled, greenish-gray color with a waxy feel to it. These rocks form by the reaction of
olivineThe mineral olivine is a magnesium iron silicate with the formula
2SiO
4...
-rich rock,
peridotiteA peridotite is a dense, coarse-grained igneous rock, consisting mostly of the minerals olivine and pyroxene. Peridotite is ultramafic, as the rock contains less than 45% silica. It is high in magnesium, reflecting the high proportions of magnesium-rich olivine, with appreciable iron...
, with water. Serpentine-rich rock forms during this reaction under a variety of conditions.
It forms near the surface of the earth, particularly where water circulates in cooling rock near
mid-ocean ridgeA mid-ocean ridge is an underwater mountain range, typically having a valley known as a rift running along its spine, formed by plate tectonics. This type of oceanic ridge is characteristic of what is known as an oceanic spreading center, which is responsible for seafloor spreading...
s: masses of the resulting serpentine-rich rock are found in ophiolites incorporated in
continental crustThe continental crust is the layer of igneous, sedimentary, and metamorphic rocks which form the continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called sial due to more felsic, or granitic, bulk composition, which lies in...
near present and past
plate tectonicPlate tectonics is a scientific theory which describes the large scale motions of Earth's lithosphere...
boundaries.
Geology
It also forms within the upper part of the Earth's
mantleThe mantle is a part of a terrestrial planet or other rocky body large enough to have differentiated by density. The interior of the Earth, similar to the other terrestrial planets, is chemically divided into layers. The mantle is a highly viscous layer between the crust and the outer core...
during
subductionIn geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. A subduction zone is an area on Earth where two tectonic plates move towards one another and...
, when crust containing wet oceanic sediments is submerged under a land mass, and water is expelled upwards into mantle
peridotiteA peridotite is a dense, coarse-grained igneous rock, consisting mostly of the minerals olivine and pyroxene. Peridotite is ultramafic, as the rock contains less than 45% silica. It is high in magnesium, reflecting the high proportions of magnesium-rich olivine, with appreciable iron...
.
The resulting serpentine-rich rock is less dense, softer, and more slippery, giving it the ability to work its way upward along fault lines. It rises through rock layers while under pressure and eventually may be exposed at the surface.
Distribution
Serpentine soils are widely distributed on Earth, in part mirroring the distribution of ophiolites. Although it covers only about 1 percent of the state's surface, the state rock of California is serpentine. One such area in California is the Edgewood Park and Natural Preserve. Serpentine soils also are present in small but widely distributed areas within the
Appalachian mountainsThe Appalachian Mountains , often called the Appalachians, are a vast system of mountains in eastern North America. Definitions vary on the precise boundaries of the Appalachians...
of eastern North America.
Serpentine endemism and bioremediation
The unique plants that survive in serpentine soils have been used in the process of
phytoremediationPhytoremediation describes the treatment of environmental problems through the use of plants which mitigate the environmental problem without the need to excavate the contaminant material and dispose of it elsewhere....
. As those plants developed specialized processes to exist in a metal-saturated environment, the process (also known as
bioremediationBioremediation can be defined as any process that uses microorganisms, fungi, green plants or their enzymes to return the natural environment altered by contaminants to its original condition. Bioremediation may be employed to attack specific soil contaminants, such as degradation of chlorinated...
) utilizes them to treat environmental problems by consuming those minerals from polluted soil.
Serpentine barrens
Serpentine barrens are a unique
ecosystemAn ecosystem consists of all the organisms living in a particular area, as well as all the nonliving, physical components of the environment with which the organisms interact, such as air, soil, water, and sunlight. It is all the organisms in a given area, along with the nonliving factors with...
found in parts of the
United StatesThe United States of America is a federal constitutional republic comprising fifty states and a federal district. The country is situated mostly in central North America, where its forty-eight contiguous states and Washington, D...
in small but widely-distributed areas of the Appalachians and the Coast Ranges of California, Oregon and Washington. The barrens occur on outcrops of altered ultramafic ophiolites.
They are named for minerals of the serpentine group, resulting in
serpentine soils, with unusually high concentrations of
ironIron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. Like other group 8 elements, it exists in a wide range of oxidation states. Iron and iron alloys are by far the most common metals and the most common ferromagnetic materials in...
,
chromiumChromium is a chemical element which has the symbol Cr and atomic number 24, first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...
,
nickelNickel is a chemical element, with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge...
and
cobaltCobalt is a hard, lustrous, gray metal, a chemical element with symbol Co and atomic number 27. Cobalt-based colors and pigments have been used since ancient times for jewelry and paints, and miners have long used the name kobold ore for some minerals.Cobalt occurs in various metallic-lustered...
. Serpentine barrens often consist of
grasslandGrasslands are areas where the vegetation is dominated by grasses and other herbaceous plants . However, sedge and rush families can also be found. Grasslands occur naturally on all continents except Antarctica...
or savannas in areas where the
climateClimates encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elements in a given region over long periods of time...
would normally lead to the growth of forests.
The ecology of serpentine barrens is poorly understood: the evolution of plants adapted to such areas and the relationship between the soil geology and ecology, particularly the ways in which plants handle high concentrations of metals such as nickel, is largely unexplored.
Examples
Rock Springs Nature Preserve in Lancaster County, PA is a 176-acre property conserved by the Lancaster County Conservancy that is a prime example of a serpentine barren. It was originally a grassland, but fire suppression led to the conversion of the area to forest. This barren contains the rare serpentine aster, as well as a number of rare species of
mothA moth is an insect closely related to the butterfly, both being of the order Lepidoptera. Moths form the majority of this order; there are thought to be 150,000 to 250,000 different species of moth, with thousands of species yet to be described...
and
skippersA skipper or skipper butterfly is a butterfly of the family Hesperiidae. They are named after their quick, darting flight habits. There are more than 3500 recognized species of skippers and they occur worldwide, but with the greatest diversity in the Neotropical regions of Central and South...
.
In Chester County, PA, the Nottingham Park Serpentine Barrens was recommended by UMCES as deserving of
National Natural LandmarkThe National Natural Landmark program recognizes and encourages the conservation of outstanding examples of the United States' natural history. It is the only natural areas program of national scope that identifies and recognizes the best examples of biological and geological features in both...
designation, on numerous grounds, including supporting a number of rare and endemic species, an intact population of
pitch pineThe Pitch Pine is a small-to-medium sized pine, native to eastern North America. This species occasionally hybridizes with other pine species such as Loblolly Pine , Shortleaf Pine , and Pond Pine The Pitch Pine (Pinus rigida) is a small-to-medium sized (6-30 m) pine, native to eastern North...
, and also the site having historic significance.
See also
- Pygmy forest
A pygmy forest is a forest which, for pedological and geological reasons, contains only miniature trees. Pygmy forests are usually associated with the coastal terraces and inner coastal mountains of Northern California....
- Serpentine
- Serpentinite
Serpentinite is a rock composed of one or more serpentine group minerals. Minerals in this group are formed by serpentinization, a hydration and metamorphic transformation of ultramafic rock from the Earth's mantle. The alteration is particularly important at the sea floor at tectonic plate...
- Ultramafic rock
Ultramafic rocks are igneous and meta-igneous rocks with very low silica content , generally >18% MgO, high FeO, low potassium, and are composed of usually greater than 90% mafic minerals...