INTRODUCTION

This chapter will show that commercial horticulture is a diverse and multidisciplinary global industry with thousands of commercial companies and organisations producing crops or offering their services to commercial customers, clients and retail consumers. These activities are carried out to satisfy local or regional demand, multinational operations or trading as vast global networks. These can vary from specialised plant growers to multiple retail chain stores; high street florist shops to seed producers and landscape contractors to tree surgeons, all supported by a wealth of research and development networks. With the world markets becoming more accessible and competitive it is essential that growers and suppliers are aware of how global issues will affect their existing customers and potential markets in the future. These factors could include fluctuating exchange rates within Europe or the sharp rise in global fuel prices, both dramatically affecting the supply and demand for crops. These variables can cause extreme difficulties for growers within an overcrowded, overstocked seasonal marketplace, especially where time-sensitive edible crops are being produced as any disruption in the supply chain will affect crop quality and its value. Many horticultural businesses can be divided into two main categories: those that sell their products or services to other commercial companies within the industry, these being wholesalers, and those that sell direct to consumers in retail nurseries, garden centres or multiple chain stores, these operate as retailers. There are companies that trade in two or more sectors, for example a wholesale production nursery supplying direct to its own onsite garden centre, or a landscape contractor growing plants for direct use in their private clients contracts.

Introduction

Conservation and sustainability go hand in hand and embrace all aspects of horticulture, from amenity to commercial and small to large scale. The gardener has a role to play whatever the size of garden. It is being increasingly recognised how important ordinary gardens are in providing a network of habitats for conserving wildlife and improving the environment.

Botanic gardens have long played a global role in conserving plant species, dating from the sixteenth century, with the first botanic garden in the UK being completed in 1663, in Oxford, (Oldfield, p. 13, 2007). This role is carried on today with traditional methods combined with the advantages of modern technology, for example at Kew’s Millennium Seedbank at Wakehurst Place, Sussex.

Many important charities have been founded to aid the conservation of plants and gardens, either as their main remit or as part of a wider theme of conservation and education, such as the National Trust and Plant Heritage. Legislation has played an increasingly important role, for example through the Wildlife and Countryside Act 1981, and Convention on International Trade in Endangered Species (CITES). Local planning authorities implement important planning legislation, for example, administering Tree Preservation Orders (TPOs).

Sustainable practices are fundamental to conservation. Again, these are important on all levels, from the compost heap and water butt in a back garden, to large-scale water storage for commercial nurseries and effective management of recycling in large parks and gardens.

So we have come to the end of our walk through ancient Israel’s library. The books of this library, collected as they are in the OT, constitute one of the most important documents of all time. The OT is an essential resource for our understanding of ancient history. It provides rich insight into human civilization before the Greco-Roman period (i.e., before Classical antiquity), and of course, the OT is especially important for a study of the history of religious thought and expression.

In this Chapter

This chapter introduces the fundamental concepts of flow in porous media. We will emphasize porous rocks with connected pore space. In many applications the flow of fluid in a porous medium is governed by Darcy’s law which states that flow velocity is proportional to the pressure gradient. The constant of proportionality is the permeability. Large porosity leads to large values of permeability.

We will consider in some detail groundwater hydrology. Important concepts are the water table and aquifers. Solutions for the extraction of water to a well will be given. Our analysis of groundwater flow can also be applied to the flow of oil and gas in porous media.

A geodynamic application is to the geometrical forms of volcanic edifices. The shape of a volcano is determined by the relative resistance to flow of magma due to its viscosity versus the gravitational resistance to vertical flows. A related geodynamic problem is magma migration at depth. Magma is produced beneath a mid-ocean ridge by pressure release melting. This melt is lighter than the solid matrix from which it was produced. The ascent of the light magma is quantified as a flow in a porous medium.

We will also consider porous media flows related to geothermal energy. The basic principles of flows associated with hot springs will be derived. Commercial geothermal facilities generally utilize two-phase (steam plus water) flows. Two-phase flows in porous media will be considered.

In addition to the OT’s fifteen books of prophecy covered in Chapters 19–21, Israel’s library also includes a distinct type of literature called “apocalyptic.” As we will see, this literature is not altogether different from prophecy. In fact, many readers believe that they are related, one (apocalypticism) as emerging from the other (prophecy). Nevertheless, apocalyptic literature is different enough to require a chapter devoted entirely to it. And the OT includes one book in its repertoire that contains in its chapters a fully developed apocalypse – the book of Daniel. This chapter will introduce the topic of ancient apocalyptic literature and will explore the OT’s examples of such literature, giving special attention to the book of Daniel.

Jerusalem fell to the Babylonians in 586 BCE. In one moment, the Judeans lost their city, their king, and their temple and priesthood. Their leadership was taken away into exile. This was obviously a turning point in Israelite history. Beyond the crisis itself, the exile lasted until 539 BCE, when the Persians captured Babylon and released the Judeans shortly thereafter. The period of the exile was likewise an important moment in history.

In this Chapter

The elastic deformation of cold rock plays an essential role in geodynamic processes. In this chapter we introduce the concepts of stress and strain. Body forces and surface stresses generate a distribution of pressure, normal stress, and shear stress in an elastic medium. The concept of isostasy is essential to the understanding of the geodynamics of topography. Isostasy provides a simple explanation for the formation of mountains and sedimentary basins. Under compressional forces the continental crust thickens, forming mountains and their crustal roots. Under tensional forces the continental crust thins, leading to surface subsidence and sedimentary basins.

Pressure and stresses cause elastic solids to deform. Dilatation, normal strain, and shear strain are measures of displacement in analogy to pressure, normal stress, and shear stress. Measurements of surface displacements (strain) are an important constraint on tectonic processes. An example is the surface strain caused by rupture on a fault. Global Positioning System (GPS) observations have revolutionized the accuracy of surface displacement measurements. Absolute positions can now be determined with an accuracy of a few millimeters.

Introduction

Plate tectonics is a consequence of the gravitational body forces acting on the solid mantle and crust. Gravitational forces result in an increase of pressure with depth in the Earth; rocks must support the weight of the overburden that increases with depth. A static equilibrium with pressure increasing with depth is not possible, however, because there are horizontal variations in the gravitational body forces in the Earth's interior. These are caused by horizontal variations in density associated with horizontal differences in temperature. The horizontal thermal contrasts are in turn the inevitable consequence of the heat release by radioactivity in the rocks of the mantle and crust. The horizontal variations of the gravitational body force produce the differential stresses that drive the relative motions associated with plate tectonics.

One of the main purposes of this chapter is to introduce the fundamental concepts needed for a quantitative understanding of stresses in the solid Earth. Stresses are forces per unit area that are transmitted through a material by interatomic force fields. Stresses that are transmitted perpendicular to a surface are normal stresses; those that are transmitted parallel to a surface are shear stresses. The mean value of the normal stresses is the pressure. We will describe the techniques presently used to measure the state of stress in the Earth's crust and discuss the results of those measurements.

In this Chapter

The concept of geochemical reservoirs in the Earth provides a basis for understanding fundamental geodynamic processes. Important reservoirs in the solid Earth include the core, mantle, and continental crust. The emphasis in chemical geodynamics is on radiogenic elements. A typical example is the decay of radiogenic rubidium 87 to strontium 87. The reference isotope is strontium 86. The ratio of strontium isotopic compositions 87/86 in a rock can be used to determine its age. One example considered is the extraction of the enriched continental crust from the depleted mantle. Volcanic processes preferentially concentrate rubidium into the continental crust. Over time the production of strontium 87 relative to the reference strontium 86 can be used to determine the mean age of the continental crust.

Introduction

Radioactive heating of the mantle and crust plays a key role in geodynamics as discussed in Section 4.5. The heat generated by the decay of the uranium isotopes 238U and 235U, the thorium isotope 232Th, and the potassium isotope 40K is the primary source of the energy that drives mantle convection and generates earthquakes and volcanic eruptions. Radiogenic isotopes play other key roles in the Earth sciences. Isotope ratios can be used to date the “ages” of rocks.

The science of dating rocks by radioisotopic techniques is known as geochronology. In many cases a rock that solidifies from a melt becomes a closed isotopic system. Measurements of isotope ratios and parent–daughter ratios can be used to determine how long ago the rock solidified from a magma and this defines the age of the rock. These techniques provide the only basis for absolute dating of geological processes. Age dating of meteorites has provided an age of the solar system of 4.57 Ga. The oldest rocks on the Earth were found in West Greenland and have an age of 3.65 Ga. Lunar samples returned by the Apollo missions have ages of over 4 Ga.

Quantitative measurements of the concentrations of radioactive isotopes and their daughter products in rocks form the basis for chemical geodynamics. Essentially all rocks found on the surface of the Earth have been through one or more melting episodes and many have experienced high temperature metamorphism.

The fifth book of the Bible is not entirely new. It isn’t simple repetition either. The Torah – both its narrative and its law – is revisited in Deuteronomy in a way that renews it for the next generation of Israelites. In doing so, the book of Deuteronomy shows that the Torah is dynamic and renewable for every generation.

In this Chapter

The purpose of this chapter is to introduce the student to the use of the computer programming language MATLAB in the context of geodynamic problems. We first present some fundamentals of using MATLAB and we then introduce some numerical methods for solving both linear and nonlinear differential equations. Integrations of both the steady and time-dependent heat conduction equations are used to illustrate the numerical approaches and their MATLAB implementations.

Introduction

Many problems in geodynamics cannot be solved analytically. Even those that can often involve complicated functions that must be evaluated numerically. Therefore, in Chapters 11 and 12 we provide the student with the tools to evaluate complex functions and mathematical expressions and produce direct numerical solutions to problems. The material can be read at any stage in going through this book, although it would be of most benefit to the student to study this chapter early on and use the tools discussed in it throughout the book. Students with a background in numerical techniques and basic computing might already be familiar with much of this material, but we have provided it with the beginning student in mind. It is not our goal in this chapter to provide a rigorous or complete introduction to numerical analysis nor is it our purpose to train students to write sophisticated numerical codes that enable the solving of geodynamical problems. Instead we offer the student a toolbox of codes to use in problem solving with some introductory discussion of the methods employed in the codes.

We have opted to use MATLAB, a computer programming language used so widely that most students will have access to it through their college or university. There are numerous books explaining the use of MATLAB and its applications in engineering and science. We will attempt to be mostly self-contained, explaining what one needs to know to employ MATLAB as a geodynamics problem-solving package.

What would you expect to find at the very beginning of Israel’s library? If Israelite authors had been focused primarily on writing a national history, we might have expected them to begin straightaway with an account of their ancestors, the patriarchs and matriarchs who became the great-grandparents of all Israel. We’ll get to that story later (Genesis 12–50). But here, in the opening chapters of the Bible, we learn that Israel’s interests are broader and deeper than that. What we have here might surprise you.

In this Chapter

We introduce the fundamental concepts of fluid mechanics. Our focus will be on mantle convection, but we will consider a variety of other geodynamic applications. These applications utilize Newtonian fluids in which the stress is proportional to the spatial gradient of velocity. The constant of proportionality is the viscosity. Solutions for isothermal problems require an equation for conservation of mass and a force balance equation. In our applications the force balance includes the pressure forces, viscous terms, and the gravitational body force. Temperature variations require addition of a buoyancy force and an energy equation. In addition to the terms included in the heat equation in Chapter 4, terms are required to account for the advection of heat (energy). Unlike the heat equation, the equations for fluid flow are usually nonlinear, for example, the product of velocity and temperature gradient in the energy equation. This nonlinearity greatly increases the difficulty of obtaining analytical solutions.

One of the important problems we will consider in this chapter is postglacial rebound. Under the load of ice during the last ice age, the continental crust was depressed in order to achieve isostatic compensation. The surface of Greenland is currently depressed below sea level due to the load of the Greenland Ice Cap. At the end of the last ice age, about 8000 years ago, large quantities of ice melted. The removal of this ice load results in a “rebound” of the Earth’s surface in order to re-establish the isostatic balance. This rebound demonstrated beyond doubt the fluid behavior of the Earth’s mantle. The rate of rebound quantified the viscosity of the mantle.

We have reserved for this chapter five relatively brief books that round out the rest of Israel’s library. Known as the “five scrolls” or the “Megilloth” (měgillôt is Hebrew for “scrolls”), these books are collected together in the “Writings” of the Jewish canon and included immediately following Psalms, Proverbs, and Job (see Figure 2.3 for this discussion). In the Christian traditions, these five scrolls are scattered among other books of the OT, based loosely on literary type. Two are included among the historical books because they are narratives (Ruth and Esther). Two are included with Job, Psalms, and Proverbs because of their poetic nature (Ecclesiastes and Song of Songs). Lamentations is grouped with Jeremiah because of the tradition that associates the book with that prophet.

After the exile ended in 539 BCE, Judah and Jerusalem were restored as a Persian administrative district known as Yehud. The last group of writing prophets comes from this period. We have gaps in our knowledge of this period of Israel’s history, which sometimes makes it difficult to read these books of prophecy. Yet some of the most important concepts of the OT emerged during this time and are preserved in these books of prophecy from the Persian period.

In this Chapter

A spherical body has a surface gravitational field that is proportional to its mass and inversely proportional to its radius squared. To a first approximation this result explains the Earth’s gravitational field. However, the Earth is rotating and this rotation results in the equatorial radius being larger than the polar radius (polar flattening and an equatorial bulge). The combination of mass and rotation gives the reference gravitational field for the Earth.

Deviations from the values given by the reference field are known as gravity anomalies. These anomalies are usually due to density variations in the Earth's interior. Surface gravity anomalies are used to search for mineral deposits and oil accumulations. We will also show that gravity anomalies can be used to quantify fundamental geodynamic processes.

Introduction

The force exerted on an element of mass at the surface of the Earth has two principal components. One is due to the gravitational attraction of the mass in the Earth, and the other is due to the rotation of the Earth. Gravity refers to the combined effects of both gravitation and rotation. If the Earth were a nonrotating spherically symmetric body, the gravitational acceleration on its surface would be constant. However, because of the Earth's rotation, topography, and internal lateral density variations, the acceleration of gravity g varies with location on the surface. The Earth's rotation leads mainly to a latitude dependence of the surface acceleration of gravity. Because rotation distorts the surface by producing an equatorial bulge and a polar flattening, gravity at the equator is about 5 parts in 1000 less than gravity at the poles. The Earth takes the shape of an oblate spheroid. The gravitational field of this spheroid is the reference gravitational field of the Earth. Topography and density inhomogeneities in the Earth lead to local variations in the surface gravity, which are referred to as gravity anomalies.