The lagoon coves in the island were formed when gigantic ice boulders melted from under the ground, for instance the Supanlahti lagoon on the westside of the island was formed this way. The vegetation in the National Park variates greatly on the different islands. Some islands are high rock cliffs, moraine and rocky land, some are treeless seagull coves, and others sandy beached esker islands. The forests are kept up and there are no rotting trees standing or on the ground. The average age of the pine forests are 75-100 years of age.
Old forests are very few.
The oldest pine forest in the National Park can be found in the middle part of Virmailansaari. On the esker islands the landscape is dominated by heaths covered with well spaced Scots pines. The groves of the upper slopes and esker summits standing on poor dry mineral soil are the specialties of the flora on Kelvenne island. Groves cover about one-tenth of the surface area. There are about 70 km of shoreline in the parks islands.