The main attraction of the Zamora region of Sanabria is the location in its interior of a lake system of glacial origin with an undoubted ecological value.
Everything is mountain and valley, forests and meadows, rocks, lagoons and waterfalls, constituting a large and unique set, with the colorful and peculiar variant of each season.
If we want to understand the park of the present landscape we must go back a few thousand years. It was then that the powerful action of the ice modeled the abrupt and spectacular environment that we contemplate today.
Most of us think of ice as a fragile solid, since we are used to seeing it only in thin layers. But when a significant thickness of ice has accumulated on the surface of the land, the ice at the bottom behaves like a plastic material, capable of sliding down a slope, which makes it an effective agent of transport, as well as an incredible modeler of the terrain. Therefore, we could define a glacier as any natural accumulation of ice on the earth, which is or was animated by a translational movement.
During the Quaternary glaciers, in the high plains of the Segundera and Cabrera mountain ranges, an extensive ice mantle was installed, from which glacial tongues radiated in all directions, especially accommodating the preglacial river valleys.
It was, therefore, a plateau glacierism in the form of a large ice cap that covered the highest parts of the two massifs, and that possibly in the coldest periods could have been linked to the glacial cirques of the León area of La Baña. When the ice retreated, the snow was concentrated in the cirques settled at the foot of the high peaks, among which the Tera was the most outstanding, reaching an ice tongue of 20 kilometers in length. The power and morphogenetic activity of the same explains the typical trough shape of the current Tera valley, which resembles the shape of a "U", i.e., a wide, narrow bottom that contrasts with almost vertical slopes. The maximum development of the glacier was reached at the confluence of the valleys of Cárdena and Segundera, where two tongues descended, thus dramatically increasing the volume of ice where the lake of Sanabria now sits. Here, the thickness of the ice was around 500m, as can be seen following the left lateral moraine, located at about 1500m altitude. Towards the east of the lake, the volume decreased rapidly, although still reaching considerable dimensions, close to 150 m thick. The pressure that this solid mass exerted on the rocky substratum is evident at the very bottom of the lake, where a threshold separates two large cavities: one 46 m deep and the other 51 m deep, which must correspond to the two centers of maximum pressure.
When the glacier retreated, the transported rocky materials were deposited frontally or laterally, drawing moraine arches of complexity and aesthetics unmatched in the rest of Spain. The frontal accumulations reached a width of about 2.5 kilometers, arranged concentrically in beautiful arches, which facilitated the damming of meltwater. The lateral moraines appear as large hills, reaching up to 6 kilometers in length. Such deposits are formed mostly by stone blocks. Some of surprising size, which are between 975 and 1600m, indicating a complex functioning of the glacial stages, as well as the accumulation processes.
Although the Sanabria Lake is the maximum expression of the modeling effect that the ice had in this area, it is not the only one perceptible to the eyes of the visitor. Thus, there are numerous lagoons distributed mainly in the high lands of Segundera and Cabrera, the result of its incisive action. We can also see numerous moraine remains scattered throughout the valleys and peaks, although in most cases they are difficult to perceive.