Physics is involved in the geological processes that occur. When a laboratory experiment is performed to emulate a natural geological process that is geophysics. When a natural process is explained using physics as described in a laboratory that too is geophysics.
The image on the right presents the results of the GRACE mission as a gravity model of the Earth.
"The Grace mission uses twin satellites to make precise gravity-field measurements to study changes on Earth. Signal achievements include the first uniform measurement of Greenland and Antarctic ice mass changes and monthly estimates of water accumulation in the world's river basins."
- 1 Theoretical geophysics
- 2 Plasma meteors
- 3 Plate tectonics
- 4 Rays
- 5 Lightnings
- 6 Sprites
- 7 Gigantic jets
- 8 Gaseous meteors
- 9 Aerometeors
- 10 Volcanic clouds
- 11 Clouds
- 12 Cumulonimbuses
- 13 Rocky meteors
- 14 Avalanches
- 15 Entrainments
- 16 Lahars
- 17 Landslides
- 18 Plucking
- 19 Rock slides
- 20 Cryoseisms
- 21 Fireballs
- 22 Bolides
- 23 Meteor showers
- 24 Cryometeors
- 25 Glaciers
- 26 Ice streams
- 27 Glacial fracturing
- 28 Surges
- 29 Glacial calving
- 30 Lithometeors
- 31 Liquid meteors
- 32 Hydrometeors
- 33 Sea levels
- 34 Rivers
- 35 Meanders
- 36 Rapids
- 37 Waterfalls
- 38 Meltwaters
- 39 Lavas
- 40 Abrasion
- 41 Chatter marks
- 42 Comminution
- 43 Flutes
- 44 Grooves
- 45 Tribology
- 46 Polish
- 47 Joints
- 48 Hypotheses
- 49 See also
- 50 References
- 51 External links
Def. the physical processes and phenomena occurring in the earth and in its vicinity is called geophysics.
Once a phenomenon has been perceived or observed the next step is to suggest possible physical processes that may be occurring to produce the phenomenon.
At beginning of the XX century, Alfred Wegener argued that there was a supercontinent called Pangea and small continents started to separate form it about 200 million years ago. Wegener proposed the continental drift hypothesis. In 1962 the sea floor spreading theory was formulated by Harry Hess. Hess established that newer seafloor is generated continuously in the oceanic ridges and the older seafloor is consumed in the oceanic trench. In 1968 both theories joined in a much more complete theory known as plates tectonics.
This idea can be defined as a postulate to explain the observed external Earth movement by the mechanism of subduction and expansion of the oceanic floor.
The upper mantle and the earth's crust behave as a strong and rigid layer called lithosphere. The lithosphere is broken into different fragments called plates which are composed of the oceanic lithosphere and the continental lithosphere. The oceanic lithosphere can vary from a few kilometres in the oceanic ridges to 100 kilometres in deep ocean basins. On the contrary, thicknesses of continental lithosphere vary between 100 and 150 kilometres. The continental lithosphere is above a ductile region of the mantle called asthenosphere.
The fragments of the lithosphere, called plates, have a relative motion and their form and size have changed constantly. Researchers recognize that seven main plates exist called: North American plate, South American plate, Pacific plate, African plate, Eurasian plate, Indo-Australian plate and Antarctic plate.
The main interactions between plates are in their boundaries. Three types of boundary plates are recognized: convergent boundary, divergent boundary and transform boundary.
- The divergent boundary, also known as a constructive boundary, is where the plates are separated and produce the elevation of material from the mantle. This mechanism creates a new ocean floor
- The convergent boundary, also known as a destructive boundary, is where an oceanic plate meets another and causes the descent of the oceanic plate. The collision could also take place between two continental plates. This mechanism creates a mountain system.
- The transform boundary, also known as a conservative boundary, is where plates slide past each other without production or destruction of the lithosphere.
The image on the right suggests that the closer the observer is to being directly underneath the aurora the more it looks like radiation spraying down. The more distant from being directly below the more the aurora looks like ribbons.
The image on the left is from a location within the auroral oval where it frequently appears directly overhead.
The temperature for a lightning bolt channel is 28 kK or 28,000 K with a peak emittance wavelength of black-body radiation at approximately 100 nm (far ultraviolet light).
"During a thunderstorm, high in the ionosphere, you’ll find an odd variety of lightning that is far above the thunderstorm itself. Jellyfish lightning, also known as sprites, are red flashes of light that last for a few seconds. They can have a wide bell-shaped top and tentacle-like wisps of light at the bottom, resembling a jellyfish."
"In high-speed videos we can see the dynamics of sprite formation and then use that information to model and to reproduce the dynamics."
"These sprites only occur during thunderstorms, though sprites are about three times higher up than storms. [...] the storms are necessary for sprites to occur, they aren’t quite sufficient enough to cause them on their own [...] The tentacle-like tendrils at the bottom were shown to form much faster than the bell-shaped top. [...] localized plasma irregularities can spark the formation of a sprite."
"On February 02, 2014, the Oro Verde Observatory (República Argentina) reported 10 or more gigantic jet event[s] observed over a thunderstorm in Entre Ríos south. Storm center [is] located at 33°S, 60°W, near the Rosario city."
Each gigantic "jet could transfer 30 coulombs of negative charge from the clouds to the ionosphere (H T Su et al. 2003 Nature 423 974)."
"During a thunderstorm in the South China Sea in July 2002, Su and co-workers used low-light-level cameras to photograph the clouds every 17 milliseconds. The five jets they observed - dubbed carrot-jets or tree-jets according to their shapes - were visible for some tens of milliseconds. But crucially, the team also detected simultaneous bursts of radio waves in four of the five cases, which indicates that the jets had transferred significant amounts of charge. The thunderclouds were at an altitude of 16 km."
"Such electromagnetic bursts have only previously been linked with powerful lightning strikes, which are known to transfer large quantities of charge. But [lightning may not have] triggered the radio waves they detected, since the local lightning detection network registered no strikes at the times of the jets."
On the left is an image of a fully developed gigantic jet above a thunderstorm near the Philippine.
Gaseous objects have at least one chemical element or compound present in the gaseous state. These gaseous components make up at least 50 % of the detectable portion of the gaseous object. Atmospheric astronomy determines whether gaseous objects have layers or spherical portions predominantly composed of gas.
Within these spherical portions may occur various gaseous meteors such as clouds, winds, or streams.
Def. a discrete unit of air, wind, or mist traveling or falling through or partially through an atmosphere is called an aerometeor.
Def. any of the high-speed, high-altitude air currents that circle the Earth in a westerly direction is called a jet stream.
Def. a system of winds rotating around a center of low atmospheric pressure the more or less violent small-scale circulations such as tornadoes, waterspouts, and dust devils is called a cyclone.
At left is an image of the cyclone Catarina.
The mushroom-shaped plume in the image on the right rose from avalanches of hot debris that cascaded down the north flank, when Mount Redoubt erupted on April 21, 1990.
"Redoubt Volcano is a steep-sided cone about 10 km in diameter at its base and with a volume of 30-35 cubic kilometers. The volcano is composed of intercalated pyroclastic deposits and lava flows and rests on Mesozoic granitic rocks of the Alaska-Aleutian Range batholith (Till and others, 1993; 1994). It has been moderately dissected by the action of numerous alpine glaciers. A 1.8-km-wide, ice-filled summit crater is breached on the north side by a northward-flowing glacier, informally known as the Drift Glacier, which spreads into a piedmont lobe in the upper Drift River Valley. The most recently active vent is located on the north side of the crater at the head of the Drift glacier. Holocene lahar deposits in the Crescent River and Drift River valleys extend downstream as far as Cook Inlet."
Def. a visible mass of
- water droplets suspended in the air,
- a group or swarm is called a cloud.
Clouds have been observed on other planets and moons within the Solar System, but, due to their different temperature characteristics, they are composed of other substances such as methane, ammonia, and sulfuric acid.
Clouds "act as electric insulators; space charge develops on the surface of the cloud and the distribution of fair-weather currents and fields in the vicinity of the cloud are altered."
The "electrical environment around clouds is such that high space charge densities can exist."
A "thunderstorm supplies a negative charge to the Earth. The net positive space charge in the air between the ground and a height of ~ 10 km is nearly equal to the negative charge on the Earth's surface".
'Giant' "thunderclouds can produce transverse electric fields of tens of microvolts per meter in the equatorial plane of the midlatitude magnetosphere."
The "contribution to global thunderstorm activity by oceanic thunderstorms should be regarded as itself having a diurnal variation of some 18% in amplitude."
"A skydiver may have captured the first film ever of a meteorite plunging down at terminal velocity, also known as its “dark flight” stage."
"The footage was captured in 2012 by a helmet cam worn by Anders Helstrup as he and other members of the Oslo Parachute Club jumped from a small plane that took off from an airport in Hedmark, Norway."
“It can’t be anything else. The shape is typical of meteorites -- a fresh fracture surface on one side, while the other side is rounded.”
“It has never happened before that a meteorite has been filmed during dark flight; this is the first time in world history.”
"Having the rock in hand would certainly help. But despite triangulations and analyses, Helstrup and his recruits still haven’t found it."
Def. a large mass or body of snow and ice sliding swiftly down a mountain side, or falling down a precipice> is called an avalanche.
Def. any of several processes in which a solid or liquid is put into motion by a fluid is called entrainment.
Def. a volcanic mudflow is called a lahar.
Part of the Mount St. Helens lahar entered Spirit Lake (lower left corner of the image on the right) but most of the flow went west down the Toutle River, eventually reaching the Cowlitz River, 50 miles (80 kilometers) downstream.
Def. "a movement of surface material down a slope" is called a landslide.
Def. the "mechanical removal of pieces of rock from a bedrock face that is in contact with glacier ice" is called plucking.
"Blocks are quarried and prepared for removal by the freezing and thawing of water in cracks, joints, and fractures. The resulting pieces are frozen into the glacier ice and transported."
Def. a falling of large amounts of rubble, earth and stones down the slope of a hill or mountain is called a rock slide.
Def. a seismic event caused by sudden glacial movements or by a sudden cracking action in frozen soil or rock saturated with water or ice is called a cryoseism.
"A cryoseism, or frost quake, is a natural phenomenon that produces ground shaking and noises similar to an earthquake, but is caused by sudden deep freezing of the ground. They typically occur in the first cold snap of the year when temperatures drop from above freezing to below zero, particularly if there is no snow cover to insulate the ground. The primary way that they are recognized is that, in contrast to an earthquake, the effects of a cryoseism are very localized. In some cases, people in houses a few hundred yards away do not notice anything. The reason that the vibrations do not travel very far is that cryoseisms don't release much energy compared with a true earthquake caused by dislocation of rock within the earth. On the other hand, since cryoseisms occur at the ground surface they can cause significant effects right at the site, enough to jar people awake. Cryoseisms typically occur between midnight and dawn, during the coldest part of the night. If conditions are right, they may occur in a series of booms and shakes over a few hours or even on successive nights."
"Cryoseisms have been reported from upstate New York, Vermont, Massachusetts, Connecticut, and Maine."
Low-frequency "vibrations [from] over a hundred quakes have happened in the last decade that aren’t along any fault line. What are they near instead? Ice. A glacier can be thought of as a very slow-moving stream. It’s made of solid ice, but over long periods of time it can flow gradually over the land, sometimes carving deep trenches and bulldozing up rock and soil. Just because it takes centuries to rearrange things, though, doesn’t mean a glacier isn’t enormously powerful at any given moment."
Numerous "low-frequency quakes in Greenland [have] been identified. [They] mostly occurred during July, August, and September. Those warmer months melt lots of glacial ice."
In the warmer months, liquid "water is pooling underneath the glacial ice to the point where the thin veneer of water at the base of the glacier allows the whole mass to slip a little [...] The quakes [may be] the vibrations set up by all that ice–in one case, six cubic miles of it–skidding as much as forty-two feet in under a minute. When that much ice scrapes, the earth itself shakes."
"The magnitude of these glacial quakes can be substantial. An ice slab roughly the size of Manhattan Island, and as tall as the Empire State building, slipping 10- meters (33 feet) causes a magnitude 5 quake."
"Furthermore, the ice quake duration can last thousands of seconds whereas a normal earthquake might last hundreds of seconds."
A "sharp increase [has occurred] in the number of quakes recorded in recent years. All 136 of the best-documented slips were traced to glaciated valleys draining the main Greenland ice sheet. A few others occurred in Alaskan glaciers or on Antarctica."
These "glacial quakes ranged from six to 15 per year from 1993 to 2002, then jumped to 20 in 2003, 23 in 2004, and 32 in 2005. This rate increase matches an increase in Greenland's temperatures."
The image on the right shows seismographs "from the Dall Glacier area of Alaska. The upper two traces (in red) are the broad band (BB) and long-period (LP) records of the M 5.0 event of September 1999. The lower two traces (in black) are the BB and LP records of an M 4.2 earthquake in the same area."
Above is a visual astronomy image of a fireball trail with some burning still visible from a meteor as it passed overhead in Chelyabinsk, Russia, on February 15, 2013.
A relatively small percentage of meteoroids hit the Earth's atmosphere and then pass out again: these are termed Earth-grazing fireballs (for example The Great Daylight 1972 Fireball).
For 2011 there are 4589 fireball records at the American Meteor Society.
"At 66 kilometers (41 miles) per second, they appear as fast streaks, faster by a hair than their sisters, the Eta Aquarids of May. And like the Eta Aquarids, the brightest of family tend to leave long-lasting trains. Fireballs are possible three days after maximum."
Def. a fireball reaching magnitude −14 or brighter. is called a bolide.
Def. a fireball reaching an magnitude −17 or brighter is called a superbolide.
Meteors may occur in showers, which arise when the Earth passes through a trail of debris left by a comet, or as "random" or "sporadic" meteors, not associated with a specific single cause. A number of specific meteors have been observed, largely by members of the public and largely by accident.
"Glacier length is the most demanding parameter regarding additional manual work and uncertainty."
"The definitions used in the former guide are:"
Def. the "average of the lengths of each tributary along its longest flowlines to the glacier snout" is called the mean length.
Def. the "longest flowline of the whole glacier" is called the maximum length.
"When a DTM of sufficient quality is available, automated techniques can be used to identify the highest glacier point and then follow the steepest downward gradient until the curvature of the glacier surface changes from concave to convex. In this region – in general, the ablation area – manual digitization close to the central flowline of the main trunk might be more efficient. For manual digitization of the length, the flowline should cross elevation contours perpendicularly. Uncertainty of the result is thereby reduced if flowline digitization starts at the lower end of the glacier."
Large apparently solid objects of ice flow. Gravity is a likely force acting on large solid ice objects. Many glaciers slide over their beds. Ice "itself can flow like a very viscous fluid, [...] increases in velocity after heavy rain [...] showed that water helps a glacier to slide. [...] the velocity is greatest in the central part and decreases progressively toward each side. [...] a glacier moves more slowly near its head and terminus than elsewhere. [...] velocity vectors do not parallel the glacier surface; relative to the surface, they are inclined slightly downward in the higher parts of the glacier, where snow accumulates, and slightly upward in the lower reaches to compensate for ice lost by melting."
Ice "moves more rapidly at the surface than at depth. [...] in general, although slow across-glacier extrusion flow sometimes occurs in narrow valleys."
There is a "time lag between the advance of the terminus and the increase in snowfall that produced it."
"Mean slope is a value that could be derived from elevation range and glacier length and was thus not listed in the guidelines by UNESCO/IASH (1970). Mean slope as derived for each glacier from the DTM with zone statistics is independent of the glacier length and refers to all individual cells of the DTM (Manley, 2008). [Mean] slope is a good proxy for other parameters like mean thickness (Haeberli and Hoelzle, 1995) [...] A large number of further parameters characterizing individual glaciers (e.g. driving stress, slope-dependent thick- ness, volume, thermal conditions, response and reaction times) can be derived or estimated from the basic parameters".
"Annual flow velocities on the Austre Torellbreen tongue [are] derived from displacement of crevasses on a pair of ASTER images (2005 and 2006) [in the image at right]: black lines – location of crevasses in 2005, white lines – location of crevasses in 2006, blue line – front position in 2005. The background image is a portion of the FCC of ASTER scene (acquired on 23.07.2006)."
The mean flow velocity of the Svalbard tidewater glacier Austre Torellbreen is 260 m yr-1.
"Examples of ASTER geocoded images (321 bands) of glaciers [in the second image on the right are] classified into different groups of flow dynamics: a) Negribreen – very slow or stagnant glacier (5.08.2003) [date surveyed 05 August 2003 at a mean flow velocity of <30 m yr-1]; b) Storbreen – slow−flowing glacier (7.08.2004) [80 m yr-1]; c) Austre Torellbreen – fast−flowing glacier (23.07.2005) [260 m yr-1]; [and] d) Perseibreen – active surge glacier (7.08.2004) [730-910 m yr-1]."
Def. "a glacier that is not moving significantly, notice lack of crevassing" is called a stagnant glacier.
Def. a glacier that is
- "moving at reasonable [a] pace",
- "has crevassing", and
- "is eroding its bed" is called an active glacier.
When the stress of the layer above exceeds the inter-layer binding strength, it moves faster than the layer below.
The geothermal heat flux becomes more important the thicker a glacier becomes.
The image on the right shows animated motions of ice flowing across Antarctica.
The second image on the right shows the ice stream velocities of Antarctic ice from zero (black) up to 250m/yr (cream white).
"Although they account for only 10% of the volume of the ice sheet, ice streams are sizeable features, up to 50 km wide, 2000 m thick and hundreds of km long. Some flow at speeds of over 1000 m per year and most of the ice leaving the ice sheet passes through them."
"Ice streams generally form where water is present, but other factors also control their velocity, in particular whether the ice stream rests on hard rock or soft, deformable sediments. At the edges of ice streams deformation causes ice to recrystallise making it softer and concentrating the deformation into narrow bands or shear margins. Crevasses, cracks in the ice, result from rapid deformation and are common in shear margins."
"Icequakes are seismic tremblings caused by sudden movement within a glacier or ice sheet, such as from a fracturing crevasse. (Anyone who has dropped an ice cube into a glass of water knows ice snaps under stress.)"
"Chile's magnitude-8.8 earthquake on Feb. 27, 2010, set off a flurry of Antarctic icequakes, each lasting from one to 10 seconds, researchers report today (Aug. 10) in the journal Nature Geoscience. The epicenter was 2,900 miles (4,700 km) north of Antarctica."
"We think the crevasses are being activated by the surface waves from this big earthquake coming through, and that's making the icequake."
Shear or herring-bone crevasses on the Emmons Glacier shown on the right often form near the edge of a glacier where interactions with underlying or marginal rock impede flow. In this case, the impediment appears to be some distance from the near margin of the glacier.
Ice cracks are also imaged in the Titlis Glacier shown on the second right.
In the third image on the right, a graduate student crosses a crevasse on the Easton Glacier, Mount Baker, in the North Cascades of the United States.
The fourth image on the right shows a crevasse on the Easton Glacier.
"Glacier mass balance is assessed in crevasses such as this on Easton Glacier. Note the horizontal horizon marking the 2007 summer surface with 3.2 m of 2008 winter snowpack on top."
"Crevasses [o]pen because of an acceleration of the glacier."
Def. "an area of rapid movement on a steep slope with extensive open crevassing" is called an icefall.
The "ice in the immediate vicinity of the shelf front is being weakened due to accumulating fractures (which may be transported from further inland), which finally leads to calving events. This calls for the incorporation of some kind of damage or fracture parameterization into ice-shelf models, in order to predict/assess their stability and possible onsetting instabilities, which have been shown to fall apart on a surprisingly short timescale."
"The great unsolved problem in ice-shelf dynamics (perhaps in the whole of glaciology) is the treatment of the shelf front."
"No response of an ice-sheet/ice-shelf system to climate variations can be computationally forecasted, unless this boundary condition is properly parameterized."
"Dynamically, an equivalent description of the calving rate – the second condition – is the relevant climatological statement, describing the mass loss of the shelf, for which only first estimates exist ... The difficulty with parameterizations of the calving rate is its inter- mittent non-smooth occurrence in nature. Such discon- tinuous behavior of the mass loss by ice shelves is most likely not adequately parameterizable, but smeared over long time scales (of decades) a smooth parameterization may well be possible".
"[A]long-flow ice shelf spreading [may be] the dominant control on calving".
The "influence of water penetrating into any crack which opens at the base of the ice shelf [is] at a pressure close to the ice overburden pressure[. It] tends to counterbalance the action of the latter as an effect opposing crack opening."
where is the water pressure at a given depth [in the figure on the left]. This change accounts for the fact that the water pressure reduces the contribution to failure of the local mean pressure in ice near the base of the ice shelf that is exposed to crevasses. It assures that damage evolution in an ice shelf always starts at the top or base, not somewhere in between."
"The largest modern surges known to have occurred on the northern hemisphere are those of Brúarjökull. During the most recent surges in 1890 and 1964 an area of 1400 km2 of the glacier was affected and the glacier advanced 8-10 km onto the forefield (Thorarinsson 1969)."
"When Brúarjökull surged, large ice-marginal moraines which can be traced over many kilometers, were produced in front of the glacier."
"The lateral changes reflected in the spatial distribution of landform assemblages are closely linked to the dynamic behaviour of Brúarjökull. Therefore it is important to understand large-scale development in ice dynamics linked to the landscape evolution. Underlying this is the importance of understanding the factors controlling the surging behaviour of the glacier."
The image on the right shows calving by the Perito Moreno Glacier, in Los Glaciares National Park, southern Argentina.
"Calving of huge, tabular icebergs is unique to Antarctica, and the process can take a decade or longer. Calving results from rifts that reach across the shelf. In the case of Antarctica's Amery Ice Shelf, the calving area resembles a loose tooth [images on the second right]."
"On a stable ice shelf, calving is a near-cyclical, repetitive process producing large icebergs every few decades. The icebergs drift generally westward around the continent, and as long as they remain in the cold, near-coastline water, they can survive decades or more. However, they eventually are caught up in north-drifting currents where they melt and break apart."
"In Greenland, floating ice tongues downstream from large outlet glaciers are more broken up by crevasses. Calving of the ice tongues releases armadas of smaller, steep-sided icebergs that drift south sometimes reaching North Atlantic shipping lanes. Calving of the large glacier, Jacobshavn, on the east coast of Greenland is responsible for the majority of icebergs reaching Atlantic shipping and fishing areas off of Newfoundland and most likely shed the iceberg responsible for the sinking of the Titanic in 1912. The Petermann Glacier in northwestern Greenland also shed a large ice island in August 2010. These denizens of the ocean are now tracked by the National Ice Center in the United States, along with other organizations."
"By 2006, the Jacobshavn Glacier [third image on the right] had retreated back to where its two main tributaries join, leading to two fast-flowing glaciers where there had previously been just one."
"The rapidly retreating Jakobshavn Glacier in western Greenland drains the central ice sheet. This image [third one on the right] shows the glacier in 2001, flowing from upper right to lower left. Terminus locations before 2001 were determined by surveys and more recent contours were derived from Landsat data. The recent stages of retreat have widened the ice front, placing more of the glacier in contact with the ocean."
"In recent years, calving of the largest ice tongues in Greenland (in particular, Jacobshavn, Helheim, and Kangerdlugssuaq) has accelerated probably due to warmer air and/or ocean temperatures. As the ice tongues have retreated, the reduced backpressure against the glacier has allowed these glaciers to accelerate significantly."
"The images [fourth set of images on the right] show a tabular iceberg calving from an ice shelf. This iceberg happens to be calving from the remnant piece of the Larsen B ice shelf at the southwestern corner of the embayment. While the Larsen B Ice Shelf underwent disintegration [...], this was a normal calving event."
"Large tabular iceberg calvings are natural events that occur under stable climatic conditions, so they are not a good indicator of warming or changing climate. Over the past several decades, however, meteorological records have revealed atmospheric warming on the Antarctic Peninsula, and the northernmost ice shelves on the peninsula have retreated dramatically (Vaughan and Doake 1996)."
"The most pronounced ice shelf retreat has occurred on the Larsen Ice Shelf, located on the eastern side of the Antarctic Peninsula's northern tip. The shelf is divided into four regions from north to south: A, B, C, and D."
Def. a suspension of dry dust in the atmosphere is called a lithometeor.
Def. the solid material thrown into the air by a volcanic eruption that settles on the surrounding areas is called tephra.
Liquid water precipitation falls from the atmosphere and reaches the ground, such as drizzle and rain. Suspended liquid water particles may form and remain suspended in the air (damp haze, cloud, fog, and mist), or may be lifted by the wind from the Earth’s surface (blowing spray) causing restrictions to visibility.
Def. precipitation products of the condensation of atmospheric water vapour are called hydrometeors.
Def. any or all of the forms of water particles, whether liquid or solid, that fall from the atmosphere are called precipitation.
Mean sea level (MSL) is a measure of the average height of the ocean's surface (such as the halfway point between the mean high tide and the mean low tide); used as a standard in reckoning land elevation. MSL also plays an extremely important role in aviation, where standard sea level pressure is used as the measurement datum of altitude at flight levels.
The upper figure at right shows the change in annually averaged sea level at 23 geologically stable tide gauge sites with long-term records as selected by Douglas (1997). The thick dark line is a three-year moving average of the instrumental records. This data indicates a sea level rise of ~27.5 cm from 1800-2000. Because of the limited geographic coverage of these records, it is not obvious whether the apparent decadal fluctuations represent true variations in global sea level or merely variations across regions that are not resolved.
For comparison, the recent annually averaged satellite altimetry data  from TOPEX/Poseidon are shown in red. These data indicate a somewhat higher rate of increase than tide gauge data, however the source of this discrepancy is not obvious. It may represent systematic error in the satellite record and/or incomplete geographic sampling in the tide gauge record. The month to month scatter on the satellite measurements is roughly the thickness of the plotted red curve.
The second figure at the right shows changes in sea level during the Holocene, the time following the end of the most recent glacial period, based on data from Fleming et al. 1998, Fleming 2000, & Milne et al. 2005. These papers collected data from various reports and adjusted them for subsequent vertical geologic motions, primarily those associated with post-glacial continental and hydroisostatic rebound. The first refers to deformations caused by the weight of continental ice sheets pressing down on the land, the latter refers to uplift in coastal areas resulting from the increased weight of water associated with rising sea levels. It should be noted that because of the latter effect and associated uplift, many islands, especially in the Pacific, exhibited higher local sea levels in the mid Holocene than they do today. Uncertainty about the magnitude of these corrections is the dominant uncertainty in many measurements of Holocene scale sea level change.
The black curve is based on minimizing the sum of squares error weighted distance between this curve and the plotted data. It was constructed by adjusting a number of specified tie points, typically placed every 1 kyr and forced to go to 0 at the modern day. A small number of extreme outliers were dropped. It should be noted that some authors propose the existence of significant short-term fluctuations in sea level such that the sea level curve might oscillate up and down about this ~1 kyr mean state. Others dispute this and argue that sea level change has been a smooth and gradual process for essentially the entire length of the Holocene. Regardless of such putative fluctuations, evidence such as presented by Morhange et al. (2001) suggests that in the last 10 kyr sea level has never been higher than it is at present.
The lower figure shows sea level rise since the end of the last glacial episode based on data from Fleming et al. 1998, Fleming 2000, & Milne et al. 2005.
At least one episode of rapid deglaciation, known as meltwater pulse 1A, is agreed upon and indicated on the plot. A variety of other accelerated periods of deglaciation have been proposed (i.e. MWP-1B, 2, 3, 4), but it is unclear if these actually occurred or merely reflect misinterpretation of difficult measurements. No other events are evident in the data presented above.
The lowest point of sea level during the last glaciation is not well constrained by observations (shown here as a dashed curve), but is generally argued to be approximately 130 +/- 10 m below present sea level and to have occurred at approximately 22 +/- 3 thousand years ago. The time of lowest sea level is more or less equivalent to the last glacial maximum. Prior to this time, ice sheets were still increasing in size so that sea level was decreasing almost continuously over a period of approximately 100,000 years.
Def. a large and often winding stream which drains a land mass, carrying water down from higher areas to a lower point, ending at an ocean or in an inland sea is called a river.
Def. a winding, crooked, or involved course or a tortuous or intricate movement of water as a stream or river is called a meander.
Def. a rough section of a river or stream which is difficult to navigate due to the swift and turbulent motion of the water is called a rapid.
On the right are rapids featuring white water before the Rhine Falls.
Def. a flow of water over the edge of a cliff is called a waterfall.
Angel Falls in the image on the left is the world's tallest at 979 m.
"On a summit flight, we were able to see the source of the meltwater stream. It appears to starts to the right of the dome where a fall face can be seen and continues down."
The image on the left shows flooding some 7.6 m deep caused by the melting of Drift Glacier.
Def. melted rock ejected by a volcano from its crater or fissured sides is called a lava.
Geologists make a distinction between magma (molten rock underground) and lava (molten rock on the surface).
Def. molten matter within the earth, the source of the material of lava flows, dikes of eruptive rocks, etc is called a magma.
"Streams of molten rock that ooze from gaps or vents in the Earth’s surface are called lava flows. Though generally slow-moving, these rivers of rock pose a hazard to everything in their paths. They can bury or burn homes and roads, ruin farmland for generations, and transform glaciers into muddy landslides (lahars)."
"Lava flows can take many shapes and move at very different rates depending on the viscosity of the magma, the slope of the land, and the rate of an eruption. Some of the speediest flows travel 60 kilometers (40 miles) per hour; the slowest creep along at less than 1 kilometer (0.6 miles) per hour. They can sometimes even flow for more than a year after an eruption has ended."
"While viscous lava flows are defined by steep flow fronts and pressure ridges, low-viscosity lavas tend to move faster and create longer, narrower shapes. They also tend to have smaller flow fronts and levee-like structure along their edges. Many characteristics of a low-viscosity lava flow are visible in [the image on the right second down] of Zhupanovsky and Dzenzursky volcanoes on Russia’s Kamchatka Peninsula. The image was acquired by the Operational Land Imager (OLI) on the Landsat 8 satellite on September 9, 2013."
"In the image, younger lava flows appear grey, while older flows are covered by green vegetation. The exact ages of the flows are unclear, but the eruptions that produced them likely occurred during the past few thousand years. Distinctive lava levees are visible along the edges of many of the younger flows. These features form as lava cools and hardens along the edges or top of a flow while the center of a flow still advances."
"In comparison to the Chao dacite in Chile (the product of viscous lava), the flows at Zhupanovsky [at lowest right] and Dzenzursky are much narrower and longer. They have smaller flow fronts (10 to 30 meters tall) in comparison to the sheer 400-meter cliffs at Chao, as well as more prominent lava levees along the edges. Like Chao, the flows shown above have pressure ridges caused by the compression of the cooling top of the lava as the flow advanced."
Def. a form of lava flow of basaltic rock, usually dark-colored with a smooth or ropey surface is called pahoehoe.
"Ropy pahoehoe [shown in the fourth image down on the right, taken 11 June 1995] is the most common surface texture of pahoehoe flows. The numerous folds and wrinkles ("ropes") that are characteristic of ropy pahoehoe form when the thin, partially solidified crust of a flow is slowed or halted (for example, if the crust encounters an obstruction or slower-moving crust). Because lava beneath the crust continues to move forward, it tends to drag the crust along. The crust then behaves like an accordian that is squeezed together--the crust is flexible enough to develop wrinkles or a series of small ridges and troughs as it is compressed and driven forward."
Def. a form of lava flow [shown on the right, fifth image down] consisting of basaltic rock, usually dark-colored with a jagged and loose, clinkery surface is called an aa.
"`A`a (pronounced "ah-ah") is a Hawaiian term for lava flows that have a rough rubbly surface composed of broken lava blocks called clinkers. The incredibly spiny surface of a solidified `a`a flow makes walking very difficult and slow. The clinkery surface actually covers a massive dense core, which is the most active part of the flow. As pasty lava in the core travels downslope, the clinkers are carried along at the surface. At the leading edge of an `a`a flow, however, these cooled fragments tumble down the steep front and are buried by the advancing flow. This produces a layer of lava fragments both at the bottom and top of an `a`a flow."
Def. an effect of mechanical erosion of rock, especially a river bed, by rock fragments scratching and scraping it is called abrasion.
The striations in the image on the right on Cerro Chirripo suggest a past glacier.
Def. "gouges [striations] cut into the bedrock by gravel and rocks carried by glacial ice and meltwater" are called glacial striations.
"Parallel striations and bedrock fracture trends (across the left side of the image [on the left]) are clearly visible in this photo [at the right]."
Def. "polished striated rock surfaces caused by one rock mass moving across another on a fault" are called slickensides.
Def. "striations or marks left on the surface of exposed bedrock caused by the advance and retreat of glacier ice" are called chattermarks.
In the image at the right is a close "up of chatter marks, Mt. Sirius, Antarctica. Lens cap in the photo is five centimeters across."
Def. a breaking or grinding up of a material to form smaller particlesis called comminution.
Def. a lengthwise groove is called a flute.
Def. a long, narrow channel or depression is called a groove.
Def. "grooves [...] cut into the bedrock by gravel and rocks carried by glacial ice and meltwater" are called glacial grooves.
Def. a force that resists the relative motion or tendency to such motion of two bodies in contact is called friction.
Def. damage to the appearance and/or strength of an item caused by use over time is called wear.
Def. application of a substance, between moving surfaces in contact in order to reduce friction and minimize heating is called lubrication.
Def. the science and engineering of interacting surfaces in relative motion; the study and application of technology using the principles of friction, lubrication and wear is called tribology.
"Grooves are gouged into the tough rock [in the image on the right] by the continental glacier that once covered the area."
"Ice won't scratch rock, of course; the sediment picked up by the glacier does the work. Stones and boulders in the ice leave scratches while sand and grit polish things smooth. The top of this outcrop looks wet, but instead it's glacial polish."
Def. a fracture in which the strata are not offset is called a joint.
Def. a fracture in rock in which (unlike a fault) the strata do not move relative to each other is called a geologic joint.
Def. a thin fracture, in sedimentary rocks, either normal or oblique to the bedding plane is called a leptoclase.
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