Accumulation results when basic processes cause a number of items to accumulate or pile up in one place. For example, a stream may during its flow encounter a depression which must fill, a lake, before the stream can continue in its course. At the end of its flow is the sea, the final accumulation. An accumulation is often a markedly different environment than the same material or materials are while on the way to the accumulations, contrast a stream, a lake, an ocean.
In addition to an accumulation of matter such as a planet, a star, a galaxy, or compressed air in a steel tank, an accumulation may be only of paths or information. A crossroads is a simple accumulation of paths, while a reference work is an accumulation of knowledge. A metropolis such as New York City is a vast, and highly significant, accumulation of people, resources, transportation, culture, and knowledge, a central node in the social, cultural, and economic network.
Accumulated precipitation, as snow, forms glaciers and ice caps. The input, at least in the past, has exceeded the output. Likewise, the continued accumulation of carbon dioxide in the atmosphere represents a failure of natural processes which remove carbon dioxide from the atmosphere to keep pace with increased input resulting from burning of fossil fuels. Likewise, accumulation of heat, occurs as the greenhouse effect is enhanced by increased accumulation of carbon dioxide.