- Differentiate the different types of glaciers and contrast them with sea ice.
- Describe how glaciers move, erode, and create landforms.
- Identify glacial erosional and depositional landforms and interpret their origin.
- Describe the history and causes of past glaciations and their relationship to climate and sea-level changes.
The hydrosphere, liquid water, is the single most important agent of erosion and deposition. The cryosphere, the solid state of water in the form of ice also has its own unique erosional and depositional features. Large accumulations of year-round ice on the land surface are called glaciers. Masses of ice floating on the ocean as sea ice or icebergs are not glaciers, although they may have had their origin in glaciers.
- 14.1: Prelude to Galciers
- Glaciers form when more snow accumulates over a long span of time than melts and eventually turns into ice. This usually occurs in mountainous areas that have both cold temperatures and high precipitation, but can also occur in extremely cold low lying areas such as Greenland and Antarctica. This chapter focuses on types of glaciers, how glaciers function, erosional and depositional landforms created by glaciers, and how glaciers are connected to past climates and modern day climate change.
- 14.2: Types of Glaciers
- There are two general types of glaciers – alpine glaciers and ice sheets. Alpine glaciers form in mountainous areas either at high elevations or near cool and wet coastal areas like the Olympic Peninsula of Washington. A common type of alpine glacier is a valley glacier which is confined to a long, narrow valley located in mountainous areas especially at higher latitudes (closer to either the north or south pole).
- 14.3: Glacier Formation and Movement
- Glaciers form when accumulating snow compresses into firn and eventually turns into ice. In some cases, perennial snow accumulates on the ground and lasts all year. This makes a snowfield and not a glacier since it is a thin accumulation of snow. Snow and glacial ice actually have a fair amount of void space (porosity) that traps air. As the snow settles, compacts, and bonds with underlying snow, the amount of void space diminishes.
- 14.4: Glacial Budget
- Glaciers gain mass during the winter as snow accumulates. During summer the snow melts. The glacier is like a bank account, if more money is coming in (snow accumulating in winter) than going out (snow melting in summer), then the bank account grows. The glacial budget works in a similar way. The glacial budget describes how ice accumulates and melts on a glacier which ultimately determines whether a glacier advances or retreats.
- 14.5: Glacial Landforms
- Glacial landforms are of two kinds, erosional and depositional landforms. Erosional landforms are formed by removing material. The internal pressure and movement within glacial ice cause some melting and glaciers to slide over bedrock on a thin film of water. Glacial ice also contains a large amount of sediments. Together, the movement plucks off bedrock and grinds the bedrock producing a polished surface and fine sediment called rock flour as well as other poorly-sorted sediments.
- 14.6: Ice Age Glaciations
- A glaciation (or ice age) occurs when the Earth’s climate is cold enough that large ice sheets grow on continents. There have been four major, well-documented glaciations in Earth’s history: one during the Archean-early Proterozoic (~2.5 billion years ago), another in late Proterozoic (~700 million years ago), another in the Pennsylvanian (323 to 300 million years ago), and the most recent Pliocene-Quaternary glaciation (Chapter 15).
Thumbnail: Ice calving from the terminus of the Perito Moreno Glacier in western Patagonia, Argentina. Image used with permission (CC-SA-BY 3.0; Luca Galuzzi).