The Pallic soils along the east coast of the North and South islands are derived from loess (fine, wind-blown sediment), and have developed during dry summers and moist winters. Cracks form in the subsoil in summer and autumn, and material is washed into them when the rains come. The subsequent expansion of the subsoil clays in winter causes compression, making the subsoil compact and restricting drainage. This soil in South Canterbury shows cracks in the subsoil filled with pale material.