The geosphere

The geosphere consists of all the solid Earth, from the soil surface, directly in contact with the atmosphere, to the mantle. It is the long-term reservoir of most of the compounds and elements that contribute to the climate system.

Direct connection between the interior of this store and the fluid envelopes of the atmosphere and ocean occurs in volcanic eruptions and hydrothermal activity. The former can, if the eruption is large, transport material and gases into the stratosphere. These can interact with the ozone layer, but more importantly, provide an effective screen to solar radiation, reducing the energy available to the climate system by reflecting back a substantial part of the incoming radiation. For example, the 1991 eruption of Mount Pinatubo in the Philippines reduced the incident radiation at Mauna Loa, a mountain top observatory in Hawaii, by just over 10% for over a year (Fig. 1.18). Similarly, the 1982 eruption of El Chichon, in Mexico, caused a decrease of over 15% for a few months.

Historically, there have been numerous occasions when volcanic eruptions caused short-term cooling of the atmosphere. The eruption of Mount Agung, in Indonesia in 1963 was probably linked to global cooling in the next year; Krakatoa in 1883 seemed to have had a similar effect. It is important, however, to note that not all large eruptions have such effects. The eruption of Mount St Helens in 1980 blew out a substantial proportion of the mountain, but the blast was directed sideways and most of the ash was put into the troposphere and quickly washed out in precipitation.

The geosphere defines the geographical boundaries of land, sea and air. We will see repeatedly how these substantially modify the radiative and circulatory climate of the atmosphere and ocean. One major impact that the geosphere has on climate is through geological change in these basic boundaries (continental drift). This will be considered in §1.8, and in more detail in Chapter 6 but the basic mechanism is contained in the theory of plate tectonics. This proposes that the upper region of the Earth, the lithosphere (the crust and the upper mantle), is composed of a number of basically stable platforms that move slowly, at the rate of up to a few centimetres per year, over the surface of the planet. These platforms, or plates, are believed to move in response to convection deeper within the Earth's interior where pressure and temperature are so high that the rock is ductile, or even fully liquid. Evidence for this interior convection is suggested by changes in the rotation period of the Earth of a few milliseconds over several decades. This would occur because of changes to the mass distribution, and hence the angular momentum, of the planet (see §2.5.2 and equation (2.9) for a discussion of angular momentum). It is known that changes in the atmospheric circulation can alter the rotation period by 1-2 milliseconds; the larger

Fig. 1.18. Variation in atmospheric transmission of solar radiation to Mauna Loa Observatory, Hawaii for two years after the eruption of Mannt Pinatubo in June 1991. The observatory is situated on a mountain top, and is therefore in the mid-troposphere. The decrease in solar transmission shows the reflection of energy by particles trapped in the stratosphere which take two years to settle out.

Fig. 1.18. Variation in atmospheric transmission of solar radiation to Mauna Loa Observatory, Hawaii for two years after the eruption of Mannt Pinatubo in June 1991. The observatory is situated on a mountain top, and is therefore in the mid-troposphere. The decrease in solar transmission shows the reflection of energy by particles trapped in the stratosphere which take two years to settle out.

Fig. 1.19. Fluctuation in the rotation period, or 'length of day', of the Earth over a 30 year period. The vertical scale is the difference, in milliseconds (10-3 s), from some average rotation period. The high frequency oscillations are atmospherically driven, for instance the peak in 1982-3 is due to the decrease in tropical easterlies allowing the planet to rotate faster during the 1982-3 El Nino (see §5.2). The longer, decadal scale, oscillation is thought to be due to motion within the Earth's interior. [Data from Hide and Dickey, 1991.]

changes observed (Fig. 1.19) are attributed to such mass re-distribution within the Earth.

This plate movement is also associated with creation and destruction of plate material (Fig. 1.20). Molten material from the Earth's lower mantle is thought to upwell into the crust, or lithosphere, along mid-ocean ridges, forming new oceanic crust which then slowly spreads out at speeds of up to 60 mm per year. This may sound extremely slow, but it means that no oceanic floor is more than about 150 million years old. To conserve the surface area of the Earth, destruction of crust must take place elsewhere. This also occurs in the ocean, in extremely deep submarine trenches. Here, oceanic crust is subducted beneath another, less dense, part of the lithosphere, typically a continental plate, and is forced to plunge steeply towards the mantle, being melted as it does so. The resulting narrow, but deep, trenches also form lengthy features on the ocean floor, practically encircling the Pacific Ocean, for instance.

Subduction zones are volcanically active, because of the energy involved in the subduction process (Fig. 1.21). Island arcs are associated with these subduction zones, such as the Hawaiian Islands in the Pacific, the Maldives in the Indian Ocean or the Scotia Ridge region of the South Atlantic sector of the Southern Ocean. Some of these arcs, such as the latter two examples, are directly associated with subduction zones, being the stable crust's response to being undercut. Others denote the former position of such zones, either of

Fig. 1.20. Schematic of a subduction zone between two oceanic plates. These are being forced towards each other by motion within the deepest layer shown. The leftmost plate is less dense than that on the right and so the crust and upper mantle (top two layers) of the right plate are pushed under the left plate. Melting of this subducting material allows the upwelling of magma to support volcanoes in the less dense plate.

Fig. 1.21. Generalized global distribution of major earthquakes since 1800. Most earthquakes are associated with modern plate boundaries or are re-activations of old plate boundaries. [Fig. 5.2 of Howell (1993), Tectonics of Suspect Terranes. Reproduced with permission of Chapman and Hall.]

Chichon Plate Boundaries

existing zones that have moved to a new position, or ones that have disappeared completely.

Plate movement and formation may also occur where two plates diverge or where an existing plate breaks up due to internal stresses. The Red Sea, with the Rift Valley in East Africa, is thought to be an ocean basin in the process of formation. The Red Sea has already experienced sufficient fissuring for two new plates to be identified, while the Rift Valley is in an earlier state of fracture.

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Responses

  • zewdi
    What is the effect of climate on the geosphere?
    8 years ago
  • SIIRI
    What effect did mauna loa have on the geosphere?
    8 years ago
  • felix
    What is the annual precipitation of geosphere?
    2 years ago
  • Kyllikki
    How are volcanoes related to the geosphere?
    2 years ago
  • pervinca took-took
    How does global warming affect the geosphere?
    1 year ago
  • giraldo greece
    How the changing climate effects the geosphere?
    1 year ago
  • emppu
    How will climate change impact the geosphere?
    1 year ago
  • Magnus
    How does climate change affect the geosphere?
    1 year ago
  • Sara Demsas
    How does the geosphere affect the ocean?
    1 year ago
  • Walter
    HOW IS THE GEOSPHERE IMPORTANT IN THE OCEAN?
    1 year ago
  • aron
    How do rising oceans affect the geosphere?
    1 year ago
  • Kaylin
    How do mid ocean ridges participate in geosphere?
    12 months ago
  • ladislao
    WHAT IS THE PACIFIC OCEAN GEOSPHERE?
    12 months ago
  • Curtis
    Does the geosphere include the worlds oceans?
    11 months ago
  • Philipp
    What is the geosohere of hawii?
    10 months ago
  • eliano
    Does the geosphere consist of solid water on earths surface?
    9 months ago
  • Flavus Twofoot
    How does the geosphere affect the flow of ocean currents?
    9 months ago
  • fikru
    How did mount st. helens effect the geosphere?
    9 months ago
  • Markus
    How does the indian ocean earthquake affect the geosphere?
    9 months ago
  • sophia saenger
    How did mauna loa effect the environment?
    8 months ago
  • kim
    What is maui's geosphere?
    8 months ago
  • abelardo
    How does an increase in emissions affect the geosphere?
    7 months ago
  • Ola Pate
    How does garbage in the ocean impact the geosphere?
    6 months ago
  • paul eisenhauer
    How does pollution effect the geosphere?
    6 months ago
  • Myrtle
    How does fish affect the geosphere?
    6 months ago
  • JOHNNY
    How does ocean pollution affect hte geosphere?
    6 months ago
  • Selam
    How will using solar energy affect the Geosphere?
    6 months ago
  • Celio Conti
    How does garbage in the ocean affect the geosphere?
    6 months ago
  • Myla Taylor
    Does global warming effect geosphere?
    6 months ago
  • Christian
    How global warming affects geosphere?
    6 months ago
  • donald
    Do mid oceanic ridges effect global warming?
    4 months ago
  • Leena
    How geosphere is afeected by climate change?
    4 months ago
  • Katja
    How does the climate system affect the geosphere?
    3 months ago
  • Marina
    How does the geosphere affect the weather 10?
    3 months ago
  • Domenica
    How do global winds affect the geosphere?
    2 months ago
  • helen
    How does water pollution affect the geosphere and biosphere?
    26 days ago
  • richard
    How does an eqrthquake affect the geosphere?
    24 days ago

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