Cracked wall. Church wall severely cracked through its bricks and mortar. Cracks such as this are usually caused by subsidence or heave of the building's foundations. Subsidence is when a building sinks, often due to waterlogged ground. Heave is the displacement of a building typically when the ground swells upwards. Cracked walls may also be caused by the growth of tree roots under a foundation. Photographed in Bristol, England.