A glacial lake is created when the glacier remains stationary for a long time and the weight of the glacier excavates the landscape. Where the glacier is less powerful, the subsoil is less excavated and rises. In addition, it is possible that a moraine (deposit of rock material that is transported with the glacier) prevents the runoff. When the ice melts, water is dammed up to the moraine and a lake is created. The Titisee owes its formation to the last ice age (Pleistocene). Up until 10,000 years ago, a glacier stretched from the Feldberg to what is now Lake Titisee. The basin carved out by the glacier and the terminal moraine form the Titisee today.