Volcanoes are exciting – yet dangerous – features, capable of reworking entire landscapes overnight. With more than a dozen volcanic eruptions occurring at different locations on Earth at any one time, volcanoes are a very real part of our world. Each of these volcanoes, and the many extinct ones around the world, has a different eruptive history. Some burst to life in explosive eruptions, like the 1991 eruption of Mt. Pinatubo in the Philippines. Others bubble up rivers of lava in what is known as an effusive eruption, like the 2018 activity on Hawai‘i’s Kilauea volcano.

This chapter will examine the landforms associated with endogenic (Earth’s internal) processes, particularly those associated with heat and which lead to eruptions of molten rock, hot water, and steam. The latter are referred to as hydrothermal processes. Therefore, we will not only discuss volcanic and plutonic landforms, but also the intriguing features associated with hydrothermal processes, such as geysers and hot springs.

As defined in Chapter 1, geomorphology is the study of landforms – plain and simple. Whether they are formed on bedrock or on loose sediment, by erosion or deposition of sediment, and whatever their age, landforms are the building blocks of Earth’s physical landscapes. In essence, landscapes are organized and interconnected assemblages of landforms. These interconnections may be temporal, genetic, or spatial. With regard to temporal connections, some landforms on a landscape may have all formed at roughly the same time. They may share a similar origin (genetic connections). On many landscapes, however, the landforms may have formed at different times and in different ways.

Who doesn’t love the beach? Beaches and coastlines are beautiful landscapes that provide a wealth of recreational, economic, and environmental benefits. In many locations, coastal areas are highly developed, which can make managing these dynamic landscapes challenging. The study of these landscapes is essential for developing land management practices that balance natural coastal processes with the challenges associated with coastal development.

Coasts are shaped by a variety of processes, such as waves, tides, and water level fluctuations. These processes operate on different timescales, ranging from short-lived storm events to sea level fluctuations that span millennia, and from local to global spatial scales. In some cases, coastal processes interact to enhance risk and vulnerability along the coast. For example, a hurricane that makes landfall at a spring (high) tide can be far more devastating than one that landfalls at a neap (low) tide.

Soil means different things to different people. To a gardener, it is a medium for plant growth. To a civil engineer, it is a type of foundational material, or perhaps something to backfill around a house or in a septic drain field. To a hydrologist, soil functions as a source of water purification and supply. To some geologists, it is the overburden that buried all the rocks! But to geomorphologists and pedologists (pedology is the study of soils), soil comprises both organic and/or mineral materials, normally at the surface, that have been altered by biological, chemical, and/or physical processes. Another recent definition stresses the importance of biota in soil formation, defining soil as the “biologically excited layer” of Earth’s crust.

Although a natural process, human actions and extreme climatic events can accentuate slope instability, leading to disastrous slope failures and loss of life, like the one that occurred in the Brazilian city of Petrópolis on February 17, 2022. Over 200 people died in the mudflows, caused by intense rainfall (258 mm in three hours) and the deforestation of upslope areas. Understanding how and why materials move downslope helps geomorphologists to predict where and when future mass movement events may occur.

Except for perhaps volcanic eruptions and earthquakes, the most impressive (and deadly) geomorphic “events” involve the downslope movement of rock, debris, and sediment – referred to as mass movements because the material moves en masse. In their simplest sense, mass movements represent the downslope transport of rock and soil materials. Examples range from massive, fast-moving landslides and debris flows, to the inexorably slow process of soil creep.

Water is central to life. Geomorphologists know that running water also plays a key role in sculpting the land surface. This chapter covers physical hydrology – the science concerned with the occurrence, distribution, and movement of water – and the movement and storage of water-borne sediment within the various Earth systems. In this chapter, we focus on streams and how they transport sediment, from source to sink. The material presented here forms an important background for Chapter 16, which focuses on landforms developed by running water.

Climate and landforms are intimately tied together. Indeed, much of geomorphology is concerned with how landforms, climate, and other surficial processes (like erosion) interact. Landforms are often studied to understand past climates, and vice versa. Thus, a complete understanding of landform genesis requires knowledge of past climates, generally termed paleoclimate.

Climate can be viewed as the prevailing weather/atmospheric conditions for a site, but over long timescales. If a geomorphologist was interested in how sand dunes in a modern desert migrate, they might look at climate over the last few decades. However, a geomorphologist interested in the origin and evolution of the entire desert would need to examine climate over tens of thousands, or even millions, of years. Thus, climate is a somewhat slippery concept, especially when one considers that climate is always changing.

Water, in all its forms, is the most important agent responsible for shaping the landscape. Some water is at the surface in rivers and lakes (surface water), but much of it eventually penetrates underground. Groundwater, present in the pore spaces of soil, regolith, and bedrock, plays a fundamental role in our lives, and (a focus of this chapter) in the dissolution of bedrock, which is perhaps the most important geomorphic effect of groundwater. Because all rocks are at least partially soluble, parts (or all) of them will dissolve and go into solution when exposed to water and its associated acids – the essence of dissolution (Fig. 12.1).

Glaciers are perennial bodies of ice and snow whose movement is driven by gravity. They vary greatly in size and morphology; most glaciers cover small areas of a mountain slope, while the largest glaciers cover entire continents! Glaciers interact with the lithosphere as they erode their beds, depressing the land below them as they grow, and allowing the lithosphere to rebound as they shrink. Along the way, glaciers are effective agents of rock weathering, erosion, transport, and deposition, and important sources of water.

Glaciers add to the natural beauty of mountain and continental landscapes, both in currently glaciated landscapes and in relict landscapes formed during past ice ages. Nonetheless, their ice and water can also pose deadly hazards.

Glacial systems include the glacier and its adjacent lakes, streams, and landscapes – a system that is also closely linked to the atmosphere.

Ice sheets have dramatically shaped the landscape across the northern regions of North America and Europe. Ice sheets are so vast that they are sometimes referred to as continental glaciers. Their deposits have directly influenced human history by rerouting river systems and by providing nutrient-rich parent materials for soils. Abundant lakes and rivers, many of which were newly formed by the ice, became early transportation arteries and supplied aquatic resources to early cultures. Indirectly, glacial sediments were transported by wind to form thick and extensive blankets of loess – home to many of the world’s best soils. Ice sheets reduced the overall relief of the landscape, as valleys were widened and filled, providing for ease of transportation, growth of agriculture, and the rise of civilizations.

Mountains are among the most prominent and inspiring landforms on Earth. Earth’s internal (tectonic, or endogenic) and external (surface, or exogenic) processes have conspired to produce a wealth of mountainous landscapes that span almost every region of our planet. No strict definition of a mountain exists, other than they rise abruptly and prominently above the surrounding land, usually in the form of peaks and ridges. Thus, mountains have considerable local relief. Some mountains may rise only a few hundred meters above sea level (asl), such as the highest mountain in the United Kingdom, Ben Nevis (1,099 m asl [above sea level]). Nonetheless, it is one of the most formidable mountains in the Scottish Highlands (Fig. 6.1A). Other mountains are far more prominent. Mount Everest, the highest point on Earth at 8,849 m asl (Fig. 6.1B), is undoubtedly the most famous of all mountains.