When the ice was melting, iron was released from the bedrock into the groundwater and became exposed iron oxide (ochre). That gave rise to a red-colour soil in some parts of Riddarhyttan, especially in the area called Röda Jorden (red earth).
The melting ice caused iron from the bedrock to enter the groundwater, forming iron oxide (ochre), leading to red soil in some parts of Riddarhyttan, especially the Röda Jorden area.