WHAT IS GEOLOGY? Vicki M. Harder

Introduction Geology is the scientific exploration of planet Earth. This exploration includes the physical, chemical, and biologic aspects of the planet. Geology can be subdivided into several areas of specialization. Two major topic areas are physical geology and historical geology. In physical geology one studies the processes that operate on Earth, both on the surface and subsurface, and the materials that the process act upon. Historical geology studies the timing of Earth events, both the physical and biologic. To these two traditional branches of geology we may now add a third, environmental geology, which encompasses aspects from both physical and historical geology in that it emphasizes the understanding of Earth processes and materials and the changes that those materials operate under. One component of environmental geology is the study of geologic hazards, that is, the wide range of geologic circumstances, materials, processes, and occurrences that are harmful, hazardous, or costly to humans. These include earthquakes, volcanic eruptions, floods, collapse and subsidence of the landscape, and landslides.

Geologic Hazards The environment is defined as the outer biophysical system in which people and other organisms exist and it is important to realize that the world is not made up of separate, isolated components. Rock, soil, sediments, water, air, and organisms must be viewed as being interconnected, and environmental geology as the study of the dynamic relationships between organisms and their physical and biologic surroundings. Environmental geology encompasses aspects from both physical and historical geology in that it emphasizes the understanding of Earth processes and materials and the changes that those materials operate under. The physical materials of the Earth have distinct physical and chemical properties that may affect their role in hazardous processes, such as the tendency to flow or to fail, or their ability to transmit seismic waves. Historical geology also contributes to the study of geologic hazards from the study of the dynamic relationships, change, between humans and Earth over time.