The main theme of Lauhanvuori–Hämeenkangas Geopark is the mire. Today’s low-lying landscape characterised by wetlands is the result of a long geological development, and its oldest features date back to 1,900 million years ago.
The geological development began when crustal movements raised a large fold mountain range through Finland. During the following hundreds of millions of years, the mountain range eroded. It left behind sand, which layered on the shore and compacted to Satakunta sandstone 1,300 million years ago, and Lauhanvuori sandstone approximately 550 million years ago.
In Lauhanvuori, crustal upheavals lifted sandstone from the shore, forming a mountain of over one kilometre in height, which eroded to its current height over time. The erosion left its traces, such as tors, in the area.
An ice age began approximately 800,000 years ago, covering the area under various ice sheets. However, the glaciers did not erode the Lauhanvuori landscape much at all. Instead, the ice piled thick moraine layers in the area.
After the ice age, the landscape was covered by the sea aside from the highest top of Lauhanvuori. The sea smoothed the moraine to well-drained sand. The fine material ended up in the sea and was transported and deposited onto the clay grounds of the surrounding valleys.
Post-glacial rebound turned the shallow sea bays into wetlands, which then developed into wet Aapa mires. Sedges started to grow in the mires. As the peat layer grew thicker, the sedges gave way to sphagnum moss. The moss formed thick layers of peat, turning the mires into raised bogs.
The mire is present in the Geopark landscape both in history and in the current time. The fields in the river alleys have been formed from wetlands, and peat bogs have been used for forestry and energy production. However, the most remote and inaccessible mires remain unaltered. Many mires drained for forestry purposes have also been restored in the past few decades.