Physical geography is one of the broadest fields and includes many areas of research. Its four main areas are lithosphere, atmosphere, hydrosphere and biosphere. Dissertation topics can easily cross those four broad categories. For example, you may wish to study the effects of "nor'easters" on beach erosion, which involves atmospheric conditions and oceanic processes. Additionally, Geographic Information Systems (GIS) may be applied to any area of research for a dissertation.
The lithosphere pertains to Earth's crust and upper mantle, both continental and oceanic. The primary research area involves plate tectonics and the resulting landforms. Tectonic dissertation topics include volcanoes, earthquakes, tsunamis, subduction and continental drift. Topics also include plate tectonic processes in the U.S. Midwest and shifting land form features of the New England Appalachian region.
Atmosphere encompasses weather, climate and ocean-atmosphere interaction. Weather research includes short-term conditions such as thunderstorms, lightning, tornadoes and El Nino, whereas climate research focuses on long-term trends for as little as 30 years to more than 150,000 years. Dissertation topics on climate research include global warming and Ice Age cycles. Ocean-atmosphere interaction research topics include hurricanes and nor'easters.
The hydrosphere is all Earth's water, including lakes, rivers and oceans. It also encompasses glaciers, rain and water vapours in clouds and fog. The effects of the hydrosphere provide a variety of dissertation topics, including coastal erosion, mass movement and flooding. Additional topics include the effects of red tide on Florida's Gulf Coast and the relationship between water quality and acid rain.
The biosphere covers all living organisms and often is called ecosystems or biomes. A biome includes all vegetation and life forms, from the smallest microbe to the largest mammals. Examples of physical geography dissertation topics on the biosphere are the effectiveness of habitat conservation plans in preserving endangered species in Costa Rican rainforests and changes in seasonal vegetation of Saguaro National Park.
Mapping changes in the environment is an appropriate method of analysis for a physical geographer. Dissertation topics include an assessment of risk associated with cliff recession, development of GIS methods to measure large, meandering rivers and visualisation of geomorphic process on landforms using local data sets. Application of a GIS model can be the focus of a dissertation or a supporting tool.