Page 49 - Fundamentals of Geomorphology

32 INTRODUCING LANDFORMS AND LANDSCAPES

ROCK AND WATER CYCLES basin water runs like this. Precipitation entering the
system is stored on the soil or rock surface, or is inter-
The Earth’s surface – the toposphere – sits at the inter- cepted by vegetation and stored there, or falls directly
faces of the solid lithosphere, the gaseous atmosphere, into a stream channel. From the vegetation it runs down
and the watery hydrosphere. It is also the dwelling-place branches and trunks (stemflow), or drips off leaves and
of many living things. Gases, liquids, and solids are branches (leaf and stem drip), or it is evaporated. From
exchanged between these spheres in three grand cycles, the soil or rock surface, it flows over the surface (overland
two of which – the water or hydrological cycle and flow), infiltrates the soil or rock, or evaporates. Once in
the rock cycle – are crucial to understanding landform the rock or soil, water may move laterally down hillsides
evolution. The third grand cycle – the biogeochemical (throughflow, pipeflow, interflow) to feed rivers, or it may
cycle – is the circulation of chemical elements (carbon, move downwards to recharge groundwater storage, or it
oxygen, sodium, calcium, and so on) through the upper may evaporate. Groundwater may rise by capillary action
mantle, crust, and ecosphere, but is less significant to to top up the rock and soil water stores, or it may flow
landform development, although some biogeochemical into a stream (baseflow), or may exchange water with
cycles regulate the composition of the atmosphere, which deep storage.
in turn can affect weathering.
Rock cycle
Water cycle
The rock cycle is the repeated creation and destruc-
The hydrosphere – the surface and near-surface waters tion of crustal material – rocks and minerals (Box 2.1).
of the Earth – is made of meteoric water.The water cycle Volcanoes, folding, faulting, and uplift all bring igneous
is the circulation of meteoric water through the hydro- and other rocks, water, and gases to the base of the atmo-
sphere, atmosphere, and upper parts of the crust. It is sphere and hydrosphere. Once exposed to the air and
linked to the circulation of deep-seated juvenile water meteoric water, these rocks begin to decompose and dis-
associated with magma production and the rock cycle. integrate by the action of weathering. Gravity, wind, and
Juvenile water ascends from deep rock layers through water transport the weathering products to the oceans.
volcanoes, where it issues into the meteoric zone for the Deposition occurs on the ocean floor. Burial of the loose
first time. On the other hand, meteoric water held in sediments leads to compaction, cementation, and recrys-
hydrous minerals and pore spaces in sediments, known tallization, and so to the formation of sedimentary rocks.
as connate water, may be removed from the meteoric Deep burial may convert sedimentary rocks into meta-
cycle at subduction sites, where it is carried deep inside morphicrocks.Otherdeep-seatedprocessesmayproduce
the Earth. granite. If uplifted, intruded or extruded, and exposed at
The land phase of the water cycle is of special inter- the land surface, the loose sediments, consolidated sedi-
est to geomorphologists. It sees water transferred from ments, metamorphic rocks, and granite may join in the
the atmosphere to the land and then from the land back next round of the rock cycle.
to the atmosphere and to the sea. It includes a surface Volcanic action, folding, faulting, and uplift may all
drainage system and a subsurface drainage system. impart potential energy to the toposphere, creating the
Water flowing within these drainage systems tends to be ‘raw relief’ on which geomorphic agents may act to
organized within drainage basins, which are also called fashion the marvellously multifarious array of landforms
watersheds in the USA and catchments in the UK. found on the Earth’s surface – the physical toposphere.
The basin water system may be viewed as a set of water Geomorphic or exogenic agents are wind, water, waves,
stores that receive inputs from the atmosphere and deep and ice, which act from outside or above the toposphere;
inflow from deep groundwater storage, that lose outputs these contrast with endogenic (tectonic and volcanic)
through evaporation and streamflow and deep outflow, agents, which act upon the toposphere from inside the
and that are linked by internal flows. In summary, the planet.