Alice said the iron of the Soul bound blood is rusting in the spokes of the wheel in her speech in Day 32 (S18-20)

#speculation Another mention of blood affecting the landscape is the Drysky desert where the Bolgroth Book mentioned iron in the blood of those who died there caused the desert to form. Perhaps the souls of those who died there are still bound to the earth?
Addition to the speculation. Darrian mentioned that the red forming in the desert is causing people to encounter it to go mad.