Ämmä Hydropower Plant
Montta hydropower plant is located about 2,5 kilometres southwest from Pyhäkoski. It was built between 1951 and 1957 by Oulujoki Power Company and designed by architect Aarne Ervi.
The construction site was challenging because Montta is located over the tectonic depression of Muhos. Due to geotechnical surveys of 1930s, it was known that the bed rock at Montta is covered with hundreds of metres of clay stone, and this again, is covered by a thick layer of moraine. Because of these conditions, builders had to use construction methods previously unseen in Finland.
The solution was the Icos Veder –method where the ground is bored with holes 60 cm in diameter. During the drilling, the holes are densified by a special Bentonite clay mixture. After this, the holes are then filled with concrete, forming a continuous concrete wall. In Montta this cut-off wall is in some places 40 metres deep, and it reaches below the moraine layer and into the clay stone. This was the first time that this method was used in Finland and because of this, it gathered widespread attention.
Montta was perhaps the power plant where Ervi’s modernist aspirations reached highest levels as he had moved on from the rigid and monumental Functionalism of Pyhäkoski and Jylhämä. Transparency and clarity, flow of light and space, curtain-like walls and the concrete frame cladded with prefabricated panels, where some of the features that underlined this. Learning from past afflictions, in Montta, Ervi was able to articulate his vision in a clear and convincing manner. The horizontal shape of the power house gives a strong sense of openness, lucidity and space.
The main mass of the power house has three monoliths, one for each machinery. The terraced block at the eastern end of the power house is reserved for the service area. The overall tectonics reveal how the structure becomes lighter in the upper floors.
The machine hall of Montta is pretty much in original condition. The striped and blue concrete floor gives the space a sense of movement while the blue back wall implicates the water as an element that is ever present and also as a source of power. The exterior wall facing the tailrace is assembled out of window elements and gives the hall its open and flowing atmosphere.
Text: Samuli Paitsola