These types of floods tend to be more common in mountainous areas where water is able to travel at higher speeds due to steep mountain slopes. Floods that are due to snow melt and ice jams are dangerous because large amounts of precipitation in the form of rain is not necessary for a flood to result. Even small amounts of rain falling on snow can lead to severe flooding. Large chunks or slabs of ice that are present in the river during times of freezing temperatures can constrict the river channel and cause the water to back up. This can often occur at points where bridges cross the river, because of the large bridge supports which are present here.
Human actions can also lead to flooding.
Today, one of the most prevalent problems dealing with flooding caused by human activity is the large amount of pavement and construction, which can lead to large amounts of runoff because the water is unable to absorbed into soil. Projects such as landfills can block streams, leading to the constriction and subsequent backing up of water. Removal of large amounts of vegetation by methods such as logging can increase the rate of runoff. Finally, the construction of manmade flood control projects can actually lead to flooding problems. Failure of manmade flood control projects such as dams can lead to extreme flooding.