Which one of the following refers to the study of the lands on the Earth?

6.07.12 Magmatic Systems

Earth's surface displays a rich diversity of igneous rock from which most other rocks are derived. The majority of igneous rocks are either ocean floor basalts or continental granitics. The processes that produce this strong bimodality are physical processes, buttressed by chemical processes, associated with a prevailing tectonic theme. Mantle convection gives rise to seafloor spreading and a distinct style of magma production and evolution in a steady-state standing magmatic mush column capped by passive thin sills. No continental silicic material is produced. The seafloor is an enormous gabbroic batholith. Silicic noise is produced within the solidification fronts of basaltic systems on small local scales. The key to accentuating and enhancing this silicic signal is through systematic reprocessing. Remelting of the oceanic crust in subduction zones, during massive bolide impacts, in areas like Iceland, and in other immobile crustal welts accumulates this silicic material into viable rock masses.

Magmatic processes in and of themselves operate within a vast array of tectonic environments, but the processes involved in the behavior and evolution of magma are finite and understandable within a clear physical and chemical framework. The key to analyzing magmatic systems is to gain an integrated physical perspective of the overall process of magma production, transport, and emplacement or eruption. Magmas chemically evolve through the gain and loss of crystals, which is governed by entrainment of exotic crystals in addition to those nucleated and grown within the magma itself. But it is the understanding of the intimate coupling of spatial physical processes with phase equilibria that furnishes the greatest insight into the true processes that shape magma and Earth itself.

6.1.3.1.3 Carbon

Earth's surface carbon cycle has been the subject of much attention due to the societal importance of that element as a fuel and a greenhouse gas. Mackenzie and Lerman (2006) and Sundquist and Visser (2003) reviewed the carbon budget of Earth's surface. The C isotopic compositions are from Heimann and Maier-Reimer (1996). The atmosphere contains 6.6 × 1016 mol C with a δ13C of ~− 8‰. The land and ocean biota contain 6 × 1016 and 0.025 × 1016 mol C, respectively, with a δ13C of ~− 25‰. The hydrosphere contains ~ 320 × 1016 mol C (most as dissolved inorganic carbon) with a δ13C value of ~ 0‰. In the crust, soils contain 24 × 1016 mol C, methane hydrates contain 83 × 1016 mol C, coal, oil, and natural gas contain 42 × 1016 mol C, sedimentary organic matter contains 105 000 × 1016 mol C, sedimentary carbonates contain 544 000 × 1016 mol C, the igneous oceanic crust contains 7660 × 1016 mol C, and the igneous-metamorphic continental crust contains 21 400 × 1016 mol C. The δ13C values of sedimentary organic matter and carbonates, which dominate the crustal budget, are ~− 25‰ and ~ 0‰, respectively.

The C/Nb atomic ratio of MORBs is ~ 1120 (i.e., CO2/Nb ~ 530 ppm ppm− 1; Cartigny et al., 2008; Saal et al., 2002). The Nb concentration of the MORB source is 1.60 × 10− 9 mol g− 1 (0.1485 ppm Nb, Workman and Hart, 2005), which translates into a C concentration of 1.79 × 10− 6 mol g− 1 (~ 79 ppm CO2). This corresponds to a lower limit on the C content of the mantle of 7.2 × 1021 mol (0.3 × 1021 kg CO2, 75 ppm CO2).

The Nb concentration in the continental crust is ~ 9 × 10− 8 mol g− 1 (8 ppm Nb, Rudnick and Gao, 2003), while that of the oceanic crust is ~ 2.7 × 10− 8 mol g− 1 (2.5 ppm Nb, Stracke et al., 2003). We thus estimate that the bulk crust contains 2.01 × 1018 mol of Nb. Using the C data from Table 1, we calculate a C/Nb atomic ratio for surface reservoirs of 3.4 × 103. The Nb concentration of the BSE is ~ 2.6 × 10− 9 mol g− 1 (0.240 ppm Nb, McDonough and Sun, 1995), the mass of the BSE (mantle + crust) is 4.03 × 1024 kg, and the BSE must contain 1.0 × 1019 mol Nb. Using a C/Nb ratio of 3.4 × 103, we calculate a C content of the BSE of 33.8 × 1021 mol. Subtracting the amount of C in surface reservoirs, we estimate that the mantle must contain at most 27 × 1021 mol C (1.2 × 1021 kg CO2, corresponding to a CO2 concentration of 300 ppm). The carbon isotopic compositions of samples from the mantle are variable with an average value of δ13C = − 5‰ (Cartigny et al., 2001; Deines, 1980; Marty and Zimmerman, 1999; Pineau and Javoy, 1983).

5.6.1.1 Components and Scales of Landscape Dynamics

Earth's surface results from the competition between deep processes induced by the tectonic system that deforms, raises, or lowers the topography, and, from surface processes controlled by the erosion-transport system that destroy the highs and fill the lows. The former deep processes are a combination of the motion of lithospheric plates and/or mantle convection, the vertical component of which moves rocks with respect to the geoid, the sea level, or a reference ellipsoid. This vertical movement is generally referred to as “rock uplift” following England and Molnar's (1990) definition. Surface processes rely on erosion, transport capacity, and sedimentation, processes that are at least dependant on potential energy, hence, on vertical motions.

Taking into account the duration of tectonics and geomorphic events, it is evident that the interactions between deep-Earth and surface-Earth systems depend on the relative rates and response times of one system with respect to the other. For that reason the relative rates and response times act on the resulting topographic evolution. For example, erosion tends to compensate rock uplift, but by definition a delay exists between both rock uplift and removal of rocks, otherwise no mountains would form.

Large-scale tectonic processes act on the whole thickness of the crust (∼30 km) or the entire lithosphere (∼100 km thick). Large-scale tectonics breaks, folds, tilts, raises, and lowers the landscape over a very large expanse of land, by more than 103−104 km2 (England and Molnar, 1990), defining in this way, the regional-scale of tectonic geomorphology. Consequently, the study of plateau uplift, regional warping and subsidence focus on extensive landmasses. More, in the understanding of plateau generation, rock uplift data only may not be a pertinent measure of plateau uplift since the surface uplift equals the rock uplift minus the erosion (or tectonic denudation) (England and Molnar, 1990; Molnar and England, 1990). Evidence of plateau uplift will be discussed in Section 5.6.2 of this chapter.

Driving mechanisms that produce plateaus uplift have received considerable attention in the literature over the past four decades, since the broad acceptance of plate tectonics are still under debate. Timing and rates of vertical movements are critical to understand which processes are the causes of the vertical forces acting on topography. Low rates of surface uplift (<0.5 mm yr−1) can be explained by crustal shortening, thickening and consequent isostatic compensation, whereas high rates of surface uplift (>0.5 mm yr−1) during one or several millions of years have their origin in mantle dynamics (Garzione et al., 2006). Mantle processes responsible for high rates of surface uplift are (among others): mantle lithosphere delamination following intracontinental subduction (Bird, 1978); convective instability of cold, dense thickened-lithospheric mantle in orogens; and, its replacement by relatively hotter and lighter mantle asthenosphere (England and Houseman, 1989; Houseman et al., 1981). This point will be elaborated in Section 5.6.3 of this chapter. The elevation history of plateaus, and how long high elevations of plateaus last, is also of great interest in order to understand the interaction between asthenospheric, lithospheric and climatic processes. Since paleoelevations can only be obtained using proxies, the way the inferred estimates of vertical motions occur are greatly interpreted and debated (e.g., Molnar, 2005).

Paleoelevation data are, in general, sparse in continental regions; generally they cover only a very small part of a plateau, preventing them being used as representative of the whole plateau (e.g., Molnar et al., 2006). Recently, new tools for paleoelevation's determination based on stable isotope paleoaltimetry (13C-18O bonds) provide new evidence for the dynamics of surface uplift and the nature of its driving mechanism in the Andes (Garzione et al., 2008; Ghosh et al., 2006b; Hoke et al., 2009) and in Tibet (Garzione, 2008). However, doubts have been shed on the reliability of this new method (Poulsen et al., 2010).

1.5 Cover Beds in the Context of the “Earth's Critical-Zone” Concept

Earth's surface is literally the fundament of all human uses of landscape. However, human influence is not restricted to the surface; rather there is much interaction with the near-surface materials, for example, in terms of nutrients and water delivered from there to crops and trees or of pollution introduced into the subsurface. For basic research, surface and subsurface are of equal interest because they make up the major interface for all Earth-surface processes.

This importance of the near-surface materials—with slope deposits being among the most widespread of these materials—has been acknowledged since decades, but this has gained much progress through the “Earth's critical zone” concept. This concept attempts integrating all ecological interdependencies from the top of the canopy layer down to and including the active phreatic zone in a holistic way. It views the subsurface as the interface between the solid materials Earth is composed of and its fluid envelopes (atmosphere, open water bodies). This is where the coevolution of landforms, soils, and biota takes place, which, on their part, affect one another as well as the critical zone as a whole through various feedback mechanisms (Brantley et al., 2006). Accordingly, this concept crosses discipline boundaries, involving essentially all fields of earth and life sciences (Brantley et al., 2007). The phenomena and processes in the critical zone are acknowledged to be crucial for sustaining life on the planet (Rasmussen et al., 2010). This book presents a close look to the composition and structure of the critical zone's solid materials on slopes and to some of the aspects regarding their role as an interface. It does not put forward an alternative concept but a concretization of the substrates and structures in the core of the critical zone.

The biomantle concept may be considered as a part of the current critical-zone concept (Johnson and Lin, 2006), although it is somewhat older (Johnson, 1990). The biomantle is defined as the upper part of the soil, which is chiefly a product of the activity of biota, where bioturbation is a dominant process in the formation of soil properties. The major advantage of this concept is its focus on the impact of organisms on near-surface materials, which had often been neglected previously. However, it is often assumed that bioturbation has even produced the “epidermal” upper part of the soils, with other processes being subsidiary at most (Johnson, 1990; Johnson et al., 2005; Paton et al., 1995; Schaetzl and Anderson, 2005).

It is well accepted among cover-bed researchers that the uppermost cover bed (the so-called upper layer) of Central Europe has been modified by the action of fauna (including man), flora, and microorganisms during the more than 10,000 years since its deposition (Frühauf, 1991; Russow and Heinrich, 2001). The interdependency between layered subsurface and vegetation has already been demonstrated by Heinrich (1991), who analyzed effects of a strong storm event that threw trees that had developed less deep rooting on nutrient-rich threefold cover-bed successions, whereas deeper rooting trees on meager twofold successions remained staying alive. However, turbation by biota alone is rarely able to explicate all differences between the materials closest to the surface and those beneath, especially if clast contents, stable-mineral composition, or other properties—outlined above to discriminate disconformities—diverge remarkably; or, if primary sediment features such as clast orientation have been preserved. Biota as many other processes of pedogenesis rather may well adapt to, and thereby accentuate und reinforce, preexisting boundaries within the soils, but not more—at least in the mid-latitudes this book focuses on.

Though known for long (e.g., Yaalon and Ganor, 1973), the addition of eolian matter to soils derived mainly from other materials may be considered as one aspect of current critical-zone research (Derry and Chadwick, 2007). This addition is often understood as a quasi-continuous process (e.g., Birkeland, 1999) although Chadwick and Davis (1990) showed that eolian addition may also have occurred in pulses. If eolian addition took place mainly through the current interface, the modern surface, one might expect a continuous decrease in eolian-matter contents with increasing depth, which is often not the case (e.g., Kleber, 2011). Rather, eolian addition may come from older, reworked materials, may be syngenetic with the deposition of the respective sediment, or may, indeed, be admixed later.

A Framework for Evaluating Change: Physical Systems

Earth's surface is dynamic, and landforms change through time in response to weathering and surface processes (e.g., erosion, mass movement, and deposition). Most of the changes occur in response to variations in the energy inputs into physical systems, including variations in rainfall intensity or total, in temperature, in river flows (discharge and sediment load), and in wave/tidal energy arriving at the coast, over a range of time-scales. Physical systems are a means of describing the interrelationships between different landforms. They form a useful spatial framework for evaluating how hazards and risks to a particular site can arise as a result of processes operating elsewhere. For example, changes in land use in the catchment headwaters can lead to changes in flood frequency and river channel change elsewhere. In addition, systems can be used to evaluate the potential impacts of a project on landforms at sites distant from the project; for example, reclamation of an intertidal wetland can have significant effects on the whole estuary, through the resulting changes to the tidal prism and mean water depth. Systems can be defined at a range of scales, from river drainage basins (watersheds or catchments) and coastal cells (sediment transport cells) to individual hillslopes, dunes, or cliffs. Irrespective of the scale, each system comprises an assemblage of individual components (i.e., the landforms) and transfers of energy and sediment (Figure 1).

Engineering geomorphology is directed towards understanding the way systems respond to relatively short- to medium-term changes in energy inputs (e.g., resulting from climatic variability, changes in sediment supply, sea-level rise, or the effects of humans), rather than to long-term landscape denudation and evolution. However, there is also a need to be aware of the significance of longer term trends (e.g., the Holocene decline in sediment availability experienced on many temperate coastlines) and the presence of potential geohazards inherited from the past (e.g., ancient landslides, periglacial solifluction sheets, karst features). Engineering project cycles are generally in the order of 10–100 years (occasionally longer), and this relatively limited duration of ‘engineering time’ imposes a constraint on the types of landscape changes that are relevant to engineering geomorphology. Abrupt and dramatic landscape changes are likely to be significant over a time-scale of 10 to ∼100 years. Relevant examples include establishment of gully systems, migration of sand dunes, river planform changes, coastal cliff recession, and the growth and breakdown of shingle barriers. High-probability to relatively high-probability events are important features and include wind-blown sand, soil erosion, shallow hillside failures, flooding, scour and river bank erosion, and coastal erosion and deposition. Low-probability events that could have a major impact on an engineering project or development are often a key issue and include flash floods, major first-time landslides, and tsunamis.

Is geography the study of land?

What is the study of Earth and its land features called?

What is the meaning of geo and graphy?

What is the science of land called?