Spontaneous memorials are a first reaction to the unanticipated, unexpected and violent loss of life. Most spontaneous memorials start within hours of death notification; someone leaves a candle or bouquet of flowers, which is often followed quickly by contributions from others. They can be the limited, personal expression of the family and friends who place flowers, candles, stuffed animals, and notes on a tree by the roadside where a fatal accident occurred, or occur on a global level.
Spontaneous memorials tend to be impermanent, but can become the place of a permanent memorial. For more on spontaneous memorials check out Holly Everett's book, Roadside Crosses in Contemporary Memorial Culture.