Scientists discovered that bogs were made by glacial deposits thousands of years ago. Many bogs began as ponds and small lakes called kettle holes that were created when glaciers began to separate from one another. These glaciers became lodged in depressions in the land and had melted by the end of the ice age. These kettle holes, lined with impermeable materials like clay, became filled with water and organic matter; soon after, unique plants like cranberries began to grow and thrive there. Present-day natural bogs, like the Tannersville Cranberry Bog in the Pennsylvania mountains, are believed to have been formed around 10,000 years ago.
Keep in mind that no two natural cranberry bogs are exactly alike. They may vary in consistency, shape, depth and size. A typical bog that might be found in a New England basin often appears as a circular pond with a floating mat of peat mosses or heath shrubs. The open water may be surrounded by sedges, dwarf shrubs and an enclosing forest of conifers. The kettle bogs can be relatively small -- or they can spread out over up to several hundred acres and measure up to 40 feet deep (12.2 km) [source: Johnson]
Many environmental factors can influence a bog's formation, but nothing's as important as a plentiful water supply. In Canada, the bog-like landscapes are vast and can spread for thousands of miles. Why? The bogs there have a nearly constantly available supply of water. On the other hand, in parts of the U.S., bogs have developed only in depressions where water collects in the basins or in low areas where drainage slows or stops completely [source: Johnson].
Interestingly, the bog's acidity, cold temperatures and lack of oxygen slows the biological activity of the bog itself. As dead matter decomposes within it, the bog becomes even more stagnant and oxygen deficient. Most bacteria and fungi cannot survive without oxygen; as a result, these agents of decay are no longer present. When something dies in a bog, it will decompose at a much slower rate and therefore could be perfectly preserved for thousands of years [source: Johnson. To put it plainly: If you're trying to dispose of something unsavory, you should look elsewhere.
Most of the bogs currently used for cranberry production are man-made. They were usually developed on natural wetlands or on uplands used to replicate the wetland environment. To thrive, each site must have an abundant supply of fresh water, access to a source of sand, the ability to hold flood water and level site topography. Environmental considerations must also be taken into account when selecting a bog site.