Ice is water frozen into a solid state. Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaque bluish-white color. In the Solar System, ice is abundant and occurs from as close to the Sun as Mercury to as far away as the Oort cloud objects. Beyond the Solar System, it occurs as interstellar ice, it is abundant on Earth's surface – in the polar regions and above the snow line – and, as a common form of precipitation and deposition, plays a key role in Earth's water cycle and climate. It occurs as frost, icicles or ice spikes. Ice molecules can exhibit more different phases that depend on temperature and pressure; when water is cooled up to three different types of amorphous ice can form depending on the history of its pressure and temperature. When cooled correlated proton tunneling occurs below −253.15 °C giving rise to macroscopic quantum phenomena. All the ice on Earth's surface and in its atmosphere is of a hexagonal crystalline structure denoted as ice Ih with minute traces of cubic ice denoted as ice Ic.
The most common phase transition to ice Ih occurs when liquid water is cooled below 0 °C at standard atmospheric pressure. It may be deposited directly by water vapor, as happens in the formation of frost; the transition from ice to water is melting and from ice directly to water vapor is sublimation. Ice is used in a variety including cooling, winter sports and ice sculpture; as a occurring crystalline inorganic solid with an ordered structure, ice is considered to be a mineral. It possesses a regular crystalline structure based on the molecule of water, which consists of a single oxygen atom covalently bonded to two hydrogen atoms, or H–O–H. However, many of the physical properties of water and ice are controlled by the formation of hydrogen bonds between adjacent oxygen and hydrogen atoms. An unusual property of ice frozen at atmospheric pressure is that the solid is 8.3% less dense than liquid water. The density of ice is 0.9167–0.9168 g/cm3 at 0 °C and standard atmospheric pressure, whereas water has a density of 0.9998–0.999863 g/cm3 at the same temperature and pressure.
Liquid water is densest 1.00 g/cm3, at 4 °C and becomes less dense as the water molecules begin to form the hexagonal crystals of ice as the freezing point is reached. This is due to hydrogen bonding dominating the intermolecular forces, which results in a packing of molecules less compact in the solid. Density of ice increases with decreasing temperature and has a value of 0.9340 g/cm3 at −180 °C. When water freezes, it increases in volume; the effect of expansion during freezing can be dramatic, ice expansion is a basic cause of freeze-thaw weathering of rock in nature and damage to building foundations and roadways from frost heaving. It is a common cause of the flooding of houses when water pipes burst due to the pressure of expanding water when it freezes; the result of this process is that ice floats on liquid water, an important feature in Earth's biosphere. It has been argued that without this property, natural bodies of water would freeze, in some cases permanently, from the bottom up, resulting in a loss of bottom-dependent animal and plant life in fresh and sea water.
Sufficiently thin ice sheets allow light to pass through while protecting the underside from short-term weather extremes such as wind chill. This creates a sheltered environment for algal colonies; when sea water freezes, the ice is riddled with brine-filled channels which sustain sympagic organisms such as bacteria, algae and annelids, which in turn provide food for animals such as krill and specialised fish like the bald notothen, fed upon in turn by larger animals such as emperor penguins and minke whales. When ice melts, it absorbs as much energy as it would take to heat an equivalent mass of water by 80 °C. During the melting process, the temperature remains constant at 0 °C. While melting, any energy added breaks the hydrogen bonds between ice molecules. Energy becomes available to increase the thermal energy only after enough hydrogen bonds are broken that the ice can be considered liquid water; the amount of energy consumed in breaking hydrogen bonds in the transition from ice to water is known as the heat of fusion.
As with water, ice absorbs light at the red end of the spectrum preferentially as the result of an overtone of an oxygen–hydrogen bond stretch. Compared with water, this absorption is shifted toward lower energies. Thus, ice appears blue, with a greener tint than liquid water. Since absorption is cumulative, the color effect intensifies with increasing thickness or if internal reflections cause the light to take a longer path through the ice. Other colors can appear in the presence of light absorbing impurities, where the impurity is dictating the color rather than the ice itself. For instance, icebergs containing impurities can appear grey or green. Ice may be any one of the 18 known solid crystalline phases of water, or in an amorphous solid state at various densities. Most liquids under increased pressure freeze at higher temperatures because the pressure helps to hold the molecules together. However, the strong hydrogen bonds in water make it different: For some pressures higher than 1 atm, water freezes at a temperature below
Pillow lavas are lavas that contain characteristic pillow-shaped structures that are attributed to the extrusion of the lava under water, or subaqueous extrusion. Pillow lavas in volcanic rock are characterized by thick sequences of discontinuous pillow-shaped masses up to one metre in diameter, they form the upper part of Layer 2 of normal oceanic crust. Pillow lavas are of basaltic composition, although pillows formed of komatiite, boninite, basaltic andesite, dacite or rhyolite are known. In general, the more felsic the composition, the larger the pillows, due to the increase in viscosity of the erupting lava, they occur wherever lava is extruded under water, such as along marine hotspot volcano chains and the constructive plate boundaries of mid-ocean ridges. As new oceanic crust is formed, thick sequences of pillow lavas are erupted at the spreading center fed by dykes from the underlying magma chamber. Pillow lavas and the related sheeted dyke complexes form part of a classic ophiolite sequence.
The presence of pillow lavas in the oldest preserved volcanic sequences on the planet, the Isua and Barberton greenstone belts, confirms the presence of large bodies of water on the Earth's surface early in the Archean Eon. Pillow lavas are used to confirm subaqueous volcanism in metamorphic belts. Pillow lavas are found associated with some subglacial volcanoes at an early stage of an eruption, they are created when magma reaches the surface but, as there is a large difference in temperature between the lava and the water, the surface of the emergent tongue cools quickly, forming a skin. The tongue continues to lengthen and inflate with more lava, forming a lobe, until the pressure of the magma becomes sufficient to rupture the skin and start the formation of a new eruption point nearer the vent; this process produces a series of interconnecting lobate shapes that are pillow-like in cross-section. The skin cools much faster than the inside of the pillow, so it is fine-grained, with a glassy texture.
The magma inside the pillow cools so is coarser grained than the skin, but it is still classified as fine grained. Pillow lavas can be used as a way-up indicator in geology. Pillow lava shows it is still in its original orientation when: Vesicles are found towards the top of a pillow; the pillow structures show a convex upper surface. The pillows might have a tapered base downwards, as they may have moulded themselves to any underlying pillows during their formation. Pillow basalt Spilite, a fine-grained igneous rock, resulting from alteration of oceanic basalt NeMO Explorer, NOAA - Contains link to video of pillows being formed
Eve Cone is a well-preserved black cinder cone on the Big Raven Plateau, British Columbia, Canada. It is one of the 30 cinder cones on the flanks of the massive shield volcano of Mount Edziza that formed in the year 700, making it one of the most recent eruptions on the Big Raven Plateau and in Canada. Eve Cone stands by itself in the middle of the Desolation Lava Field and its distinctive shape can be seen from a long distance. Photographed, Eve Cone is covered by light yellow pumice from a close by but unknown vent. List of volcanoes in Canada List of Northern Cordilleran volcanoes Northern Cordilleran Volcanic Province Volcanism of Canada Volcanism of Western Canada "Eve Cone". BC Geographical Names
Geographic coordinate system
A geographic coordinate system is a coordinate system that enables every location on Earth to be specified by a set of numbers, letters or symbols. The coordinates are chosen such that one of the numbers represents a vertical position and two or three of the numbers represent a horizontal position. A common choice of coordinates is latitude and elevation. To specify a location on a plane requires a map projection; the invention of a geographic coordinate system is credited to Eratosthenes of Cyrene, who composed his now-lost Geography at the Library of Alexandria in the 3rd century BC. A century Hipparchus of Nicaea improved on this system by determining latitude from stellar measurements rather than solar altitude and determining longitude by timings of lunar eclipses, rather than dead reckoning. In the 1st or 2nd century, Marinus of Tyre compiled an extensive gazetteer and mathematically-plotted world map using coordinates measured east from a prime meridian at the westernmost known land, designated the Fortunate Isles, off the coast of western Africa around the Canary or Cape Verde Islands, measured north or south of the island of Rhodes off Asia Minor.
Ptolemy credited him with the full adoption of longitude and latitude, rather than measuring latitude in terms of the length of the midsummer day. Ptolemy's 2nd-century Geography used the same prime meridian but measured latitude from the Equator instead. After their work was translated into Arabic in the 9th century, Al-Khwārizmī's Book of the Description of the Earth corrected Marinus' and Ptolemy's errors regarding the length of the Mediterranean Sea, causing medieval Arabic cartography to use a prime meridian around 10° east of Ptolemy's line. Mathematical cartography resumed in Europe following Maximus Planudes' recovery of Ptolemy's text a little before 1300. In 1884, the United States hosted the International Meridian Conference, attended by representatives from twenty-five nations. Twenty-two of them agreed to adopt the longitude of the Royal Observatory in Greenwich, England as the zero-reference line; the Dominican Republic voted against the motion, while Brazil abstained. France adopted Greenwich Mean Time in place of local determinations by the Paris Observatory in 1911.
In order to be unambiguous about the direction of "vertical" and the "horizontal" surface above which they are measuring, map-makers choose a reference ellipsoid with a given origin and orientation that best fits their need for the area they are mapping. They choose the most appropriate mapping of the spherical coordinate system onto that ellipsoid, called a terrestrial reference system or geodetic datum. Datums may be global, meaning that they represent the whole Earth, or they may be local, meaning that they represent an ellipsoid best-fit to only a portion of the Earth. Points on the Earth's surface move relative to each other due to continental plate motion and diurnal Earth tidal movement caused by the Moon and the Sun; this daily movement can be as much as a metre. Continental movement can be up to 10 m in a century. A weather system high-pressure area can cause a sinking of 5 mm. Scandinavia is rising by 1 cm a year as a result of the melting of the ice sheets of the last ice age, but neighbouring Scotland is rising by only 0.2 cm.
These changes are insignificant if a local datum is used, but are statistically significant if a global datum is used. Examples of global datums include World Geodetic System, the default datum used for the Global Positioning System, the International Terrestrial Reference Frame, used for estimating continental drift and crustal deformation; the distance to Earth's center can be used both for deep positions and for positions in space. Local datums chosen by a national cartographical organisation include the North American Datum, the European ED50, the British OSGB36. Given a location, the datum provides the latitude ϕ and longitude λ. In the United Kingdom there are three common latitude and height systems in use. WGS 84 differs at Greenwich from the one used on published maps OSGB36 by 112 m; the military system ED50, used by NATO, differs from about 120 m to 180 m. The latitude and longitude on a map made against a local datum may not be the same as one obtained from a GPS receiver. Coordinates from the mapping system can sometimes be changed into another datum using a simple translation.
For example, to convert from ETRF89 to the Irish Grid add 49 metres to the east, subtract 23.4 metres from the north. More one datum is changed into any other datum using a process called Helmert transformations; this involves converting the spherical coordinates into Cartesian coordinates and applying a seven parameter transformation, converting back. In popular GIS software, data projected in latitude/longitude is represented as a Geographic Coordinate System. For example, data in latitude/longitude if the datum is the North American Datum of 1983 is denoted by'GCS North American 1983'; the "latitude" of a point on Earth's surface is the angle between the equatorial plane and the straight line that passes through that point and through the center of the Earth. Lines joining points of the same latitude trace circles on the surface of Earth called parallels, as they are parallel to the Equator and to each other; the North Pole is 90° N. The 0° parallel of latitude is designated the Equator, the fun
Volcanic history of the Northern Cordilleran Volcanic Province
The volcanic history of the Northern Cordilleran Volcanic Province presents a record of volcanic activity in northwestern British Columbia, central Yukon and the U. S. state of easternmost Alaska. The volcanic activity lies in the northern part of the Western Cordillera of the Pacific Northwest region of North America. Extensional cracking of the North American Plate in this part of North America has existed for millions of years. Continuation of this continental rifting has fed scores of volcanoes throughout the Northern Cordilleran Volcanic Province over at least the past 20 million years and continued into geologically recent times. Eruptive activity in the Northern Cordilleran Volcanic Province throughout its 20 million year history has been the production of alkaline lavas, including alkaline basalts. A range of alkaline rock types not found in the Western Cordillera are regionally widespread in the Northern Cordilleran Volcanic Province; these include nephelinite and peralkaline phonolite and comendite lavas.
The trachyte and comendite lavas are understood to have been created by fractionation of alkali basalt magma in crustal reservoirs. An area of continental rifting, such as the Northern Cordilleran Volcanic Province, would aid the formation of high-level reservoirs of capable size and thermal activity to maintain long-lived fractionation. In the past 15 million years, at least four large volcanoes have formed their way through dense igneous and metamorphic composed bedrock of this part of North America; this includes Hoodoo Mountain, the Mount Edziza volcanic complex, Level Mountain and Heart Peaks, which are located in northwestern British Columbia. Most notable of these is the 7.5 million year old Mount Edziza volcanic complex, which has had more than 20 eruptions in the past 10,000 years. The only activity present in the Northern Cordilleran Volcanic Province has been occasional earthquakes and constant boiling of hot springs. However, a high potential exists for renewed eruptive activity that could threaten life and property in the volcanic zone.
More than 100 eruptions have occurred in the past 20 million years with a broad range of eruptive styles. These volcanic processes have created a range of different volcanic landforms, including stratovolcanoes, shield volcanoes, lava domes and cinder cones, along with a few isolated examples of rarer volcanic forms such as tuyas. Large persistent volcanoes of the Northern Cordilleran Volcanic Province can remain dormant for hundreds or thousands of years between eruptions and therefore the greatest risk caused by volcanic activity is not always apparent. Volcanics older than 14 million years are found in the northern portion of the volcanic province while volcanics ranging from nine to four million years old exist only in the middle of the volcanic province. At least three types of volcanic zones are present in the Northern Cordilleran Volcanic Province, including large persistent lava plateaus like those found at the Mount Edziza volcanic complex, polygenetic volcanoes such as Hoodoo Mountain and monogenetic volcanoes like the basaltic cinder cones found throughout the volcanic province.
When Northern Cordilleran volcanoes do erupt, pyroclastic flows, lava flows and landslides can devastate areas 10 km away and mudflows of volcanic ash and debris can inundate valleys 10 km downstream. Falling ash from explosive eruptions can disrupt human activities hundreds of kilometres downwind, drifting clouds of fine volcanic ash can cause severe damage to jet aircraft hundreds of kilometres away. Volcanic deposits in the Northern Cordilleran Volcanic Province include lava flows and unwelded pyroclastic deposits, hydroclastic deposits and other ice-contact volcanic deposits; the variety of different volcanic deposits is due to changes in eruption characteristics from subaerial eruptions to broadly subglacial eruptions throughout the history of the Northern Cordilleran Volcanic Province. There is evidence of a decline in volcanic activity over the past few million years; this decline in volcanic activity can be grouped into two phases. From eight to four million years ago, volcanism rates were higher.
Magma production during this volcanic phase was most active from seven to five million years ago and was related to a period of rifting along the Pacific and North American Plate boundary. Between four and three million years ago in the Pliocene epoch, a pause in volcanic activity began to happen; the most recent magmatic phase ranging from two million years ago to present resulted from nearby areas of rifting during a period of compression between the Pacific and North American plates. Volcanism rates during this volcanic phase was most active from two to one million years ago with the construction of 25 volcanic zones decreased one million years ago with the construction of 11 volcanic zones. To date, the most recent volcanic phase has produced 100 km3 of volcanic material whereas the first phase produced 250 km3 of volcanic material. Though the rate in volcanism throughout the Northern Cordilleran Volcanic Province has changed there is no correlation between the rate in magma production and the number of active volcanoes during any interval of time.
The present day volcanism rate for the Northern Cordilleran Volcanic Province is lower than the Cascade Volcanic Arc and Hawaiian volcanism rates. However, geologists are aware the temporal volcanic patterns known for the Northern Cordilleran Volcanic Province should be looked at because volcanics that pre-date the last glacial period have been eroded by glacial ice and many of the volcanics have not been directly dated or have not been dated