Marmitas from Gigante do Caima

Geossítio 4 Marmitas from Gigante do Caima

Where the water shapes the stone…

People say that “water soft on a hard stone, hit hard until it breaks”. So it is with the giant marmitas: depressions found in the rocky bottom of the river. These structures are the result of the dynamics generated after periods of rain that lead to an increase in the flow of the River Caima. As a result, the energy of the water becomes greater and is capable of transporting sand and rocky blocks of varying sizes (sediment). As you walk along the river valley, from the bridge over the Caima River to the village of Mizarela, you can see that the Marmitas de Gigante (Giant’s Mounds) are formed in granite rock, becoming increasingly numerous, wider and deeper as you get closer to the point where the Frecha da Mizarela waterfall occurs. The River Caima, which forms not far from here, from the confluence of the various watercourses in the interior of the mountain plateau, will flow into the River Vouga. The “Filhos da Freita Marathon” trail race also passes through here.

Informação Geológica

The marmitas originate in the irregularities of the river’s rocky bed, which develops upstream of the Frecha da Mizarela waterfall on the Granite of Serra da Freita, a leuco to mesocratic rock, with a phaneritic texture and medium grain, about 310 million years old. These irregularities retain some sediment in their vicinity. The accumulation of sediment will, in turn, cause a swirling movement of the water, whose kinetic energy promotes a circular movement. Little by little, due to friction, the sediment digs more or less circular depressions in the bed of the river Caima, within which it becomes trapped. Over time, the depressions get larger and the pebbles inside tend to become smaller and rounder. These depressions always face upwards and can appear alone or in groups along a fracture line. In the latter case, over time, the depressions can coalesce to form water flow channels.