Deltas and estuaries are dynamic systems associated with the mouths of rivers. Deltas are accumulations of river-derived sediment whereas estuaries are the tide-influenced lower parts of rivers and their valleys. The distinction between them is sometimes difficult to discern, and it is useful to consider a continuum of deltaic–estuarine landforms. Deltaic–estuarine morphology is influenced by geological setting and topography, and landforms are shaped by hydrodynamic processes. Riverine and coastal sediments are affected by both alluvial and marine influences, together with minor local processes, such as direct input of colluvium from hillslopes, cliff retreat, wind redistribution of sediment, and chemical and biological action.

River discharge and the rate of delivery of sediment to the ocean or embayment vary in relation to catchment size, lithology and climate (Milliman, 2001). The rivers that drain from the continental area of southern and eastern Asia, with highly tectonic hinterlands and prominent monsoon climates, for instance, deliver large volumes of sediment to the oceans (Milliman and Meade, 1983). However, steep, tectonically active island catchments, such as those throughout the Indonesian island arc, also contribute disproportionately large sediment volumes to the ocean (Milliman and Syvitski, 1992).

This book outlines the way that coasts operate. It is written for students of coastal geomorphology, coastal environments, and coastal geology, and for all those with an interest in coastal landforms or who seek insights into the way the coast behaves. It brings together studies of process operation and studies of coastal evolution concerned with longer-term landform development, into morphodynamic models. Coastal morphodynamics involves the mutual co-adjustment of process and form. It provides a framework from which to generalise across space and time scales. The book introduces these concepts and outlines geological setting, materials and coastal processes. Although there are physical principles which govern the response of sediment to forcing factors such as wave energy, the complexity of non-linear interactions means that it is generally difficult to scale up to explain behaviour over time scales that are relevant to human societies.

The book is based heavily on my own research experiences in Australia, Britain, the United States, New Zealand and on many islands in the West Indies, Pacific and Indian Oceans. It also draws extensively on the scientific literature and pays particular tribute in terms of historical perspective to those coastal scientists who have built the foundations of what we know. I hope that it instils something of the sense of wonder that I feel about the coast, and offers new perspectives on how the coast is shaped.

Coasts are often highly scenic and contain abundant natural resources. The majority of the world's population lives close to the sea. As many as 3 billion people (50% of the global total) live within 60 km of the shoreline. The development of urbanised societies was associated with deltaic plains in semiarid areas, and the first cities appeared shortly after the geomorphological evolution of these plains (Stanley and Warne, 1993a). The coast plays an important role in global transportation, and is the destination of many of the world's tourists.

The shoreline is where the land meets the sea, and it is continually changing. Coastal scientists, and the casual ‘wanderer by the shore’, have attempted to understand the shoreline in relation to the processes that shape it, and interrelationships with the adjacent shallow marine and terrestrial hinterland environments. Explaining the geomorphological changes that are occurring on the coast is becoming increasingly important in order to manage coastal resources in a sustainable way.

This book examines the coast as a dynamic geomorphological system. Geomorphology is the study of landforms, and coastal geomorphology is concerned primarily with explaining the many different types of coastal landforms, and understanding the factors that shape them.

Beaches represent some of the most dynamic coasts; they are attractive, not only from aesthetic and recreational points of view, but also as field areas for geomorphological research. The term beach describes wave-deposited sediment. As sediments continue to accrete on beaches they build a larger feature much of which is no longer actively reworked by waves, termed a barrier.

Coastal landforms adjust towards, but rarely find, delicate and dynamic balances with the processes that operate. This is expressed very clearly in the above quotation from G.K. Gilbert, and has been a recurrent theme in the preceding chapters.

Rocky coasts occur where rugged or relatively resistant terrestrial lithology abuts the ocean, forming a distinct or abrupt transition between land and sea. They are typically high-energy coasts, primarily of sea cliffs and other steeply inclined shorelines, on which the influence of underlying rock type is plainly apparent. Many of these coasts evolve at slow rates; in places, resistant pre-Tertiary rocks appear to have changed little over millions of years. However, it is clear that tectonic activity and fluctuations of sea level, particularly during the Quaternary, have caused shoreline position to adjust over time.

Coasts composed predominantly of mud, comprising silt and clay-sized sediment, occur in low-energy settings, generally sheltered from wave action. Muddy coasts can be part of, or adjacent to, deltaic–estuarine coasts as described in the previous chapter, and are usually dominated by tides. Fine sediments are transported considerable distances in suspension but if subject to flocculation into low-density deformable aggregates can behave like larger particles. After deposition, muddy sediments tend to be cohesive, making them more resistant to resuspension, and highly organic, supporting a diverse biota.

On muddy coasts, sediments become finer onshore in contrast to beach and barrier coasts which become coarser onshore. Mudflats characterise much of the intertidal zone, but the lower intertidal and subtidal zones tend to contain extensive sandy deposits. The upper intertidal and supratidal zones often support halophytic (salt-tolerant) vegetation, comprising mangroves on tropical shorelines but dominated by salt marshes in mid and high latitudes.

The coastal system operates within a series of boundary conditions. Geological setting and materials exert primary controls on the range of landforms that can be formed by coastal processes. The plate-tectonic setting is important in terms of vertical and horizontal movements over the long-term evolution of a particular coast. Climate affects the rate at which terrestrial and oceanographie processes operate, and is linked to sea-level change. Relative changes of sea level constrain shoreline position and geomorphological process operation, and influence how the coast is shaped at a range of scales. Lithology and the materials from which the coast is composed are also important.

This chapter examines factors that constitute boundary conditions, adopting a geological time-scale perspective, and then examining conditions at increasingly smaller temporal and spatial scales. Plate-tectonic setting influences long-term vertical and horizontal displacements of land relative to sea level. Fluctuations in the level of the sea influence the way in which the land is abraded by marine processes. In some cases, these can be deciphered from terraces or shelves or from sequences of sediments that have been deposited. The significance of sea-level changes at geological time scales, especially through the Quaternary, has been widely accepted.

Coastal landforms are shaped by a range of processes. This chapter examines the principal sources of energy by which these materials are moved. The processes are considered individually, although in practice a stretch of coast is likely to be influenced by several processes, acting simultaneously or in sequence. A modern coastline is the outcome of processes that operate today and those that have operated over time, and many landforms have been partially or wholly inherited from former conditions.

Coastal landforms can be composed of rocks or sediments, as indicated in the previous chapter. The movement of sediment is a primary control on coastal morphodynamics and this chapter begins with a consideration of the sedimentary processes involved with erosion, transport and deposition of this material.

The principal source of energy for most coastal systems comes from waves. The generation of waves and their transformation as they approach the shore are described.

Authenticity of 1056–80

Long before anyone suggested that Medea 1056–80 were interpolated, that is, added by an actor/director other than Eur. in a performance later than 431 bce, there had been scholarly speculation about two recensions of the play by Eur. himself. This theory derived from Paolo Manuzio's observation of the absence in our text of a line of Ennius' Medea (fr. CV Jocelyn: qui ipse sibi sapiens prodesse non quit nequiquam sapit) that he wrongly identified as an exact version of Eur. fr. 905 (Cicero, ad Fam. 13.15.2: μισῶ σοϕιστὴν ὅστις οὐχ αὑτῶι σοϕός), and it received some support from remarks by Porson, Boeckh, and others, but by 1875 most of the passages referred to this Euripidean revision were satisfactorily explained in other ways. Already in the first edition of his school commentary Wecklein had developed the theory that Eur., some years earlier than 431, wrote a version of Medea fundamentally similar in conception to the play of 431, and that this earlier version inspired Neophron's imitation, produced before 431 as well (and thus in the festival records as earlier than Eur.'s play, misleading Aristotle and Dicaearchus: see Introd. 5). It was in the context of such theories that Bergk proposed that lines 1056–80 were to be regarded as a (Euripidean) doublet of 1040–55.

Medea is probably now the play of Euripides most widely known to the general public, from exposure to translations in classes in secondary schools and colleges and from performances either of translations of the Greek text or of looser adaptations of the plot. In the curriculum of programmes in ancient Greek, too, Medea is frequently an assigned text for study in the original language, and is sometimes the first Greek drama or first Greek poetry that a learner studies. In earlier generations, the play was equally studied but often frowned upon, for unAristotelian motivation and causation, for the extremity of Medea's action, and for the moral shock of its conclusion. In more recent times, the play has deservedly attained a better reputation, as critics and audiences have become more open to acknowledging the tensions and contradictions of classical Greek culture, to appreciating the chaotic as well as the harmonious and serene. Rather than seeing Medea as a realistic or psychological study, scholars now concentrate on issues like the problematics of the heroic code, the religious and ethical aspects of revenge, oath, and supplication, and the socio-political tensions reflected in the contest of genders and ethnicities evoked by the play.

The goal of this commentary is to make the play accessible in all its complication and sophistication to present-day students. It aims to provide, on the one hand, the linguistic and technical information that will support the task of translation and equip the student to appreciate the formal and artistic devices of Greek tragedy: hence, the sections Language and Style, and Prosody and Metre that follow the General Introduction.

Prologue

The opening scenes of the play (‘prologue’ in the wider sense defined in Poetics 12, 1452b19–20, as ‘the whole portion of the drama preceding the entrance-song of the chorus’: SE 2) offer some sparing hints of the past history, expose the distraught and emotional state of Medea under the pressure of Jason's betrayal, and introduce the new event (the decree of exile) that motivates the action (conceived, as usual for Greek tragedy, as events completed within a single day: Poetics 1449b12–13). The sequence may be divided into three parts by variations in form and by entrances and exits (SE 2): 1–48 nurse alone in iambic monologue, 49–95 (entrance during 45–9) iambic dialogue of nurse and tutor (with silent boys), 96–130 (gradual departure indoors during 89–105: 89n.) anapaests, chanted by nurse outdoors and sung by Medea indoors. This third part in fact flows almost seamlessly into the parodos (SE 2), since the chorus' lyric is interspersed with more anapaests from both the nurse and Medea, the chorus being alone only for 204–13.

Monologue of the nurse

Eur. routinely begins his plays with a single speaker addressing the audience more or less directly, a technique that permits the clear presentation of background details and that openly acknowledges the theatrical situation and the role of the audience as interpreters witnessing an enacted sequence of events (compare the remarks of Aristophanes' ‘Euripides’ in Frogs 946–7, 1122).