How to tell if the ground under your house is moving

Landslides have a reputation for striking without warning. Most of them do not. What actually happens is that the warning arrives disguised as a maintenance problem, and gets treated as one.

A door that sticks in winter, a crack across the driveway, a fence gone crooked. Any of those alone is a normal house getting older. Several of them appearing on the same slope over the same few weeks is the ground telling you something.

The slow signs: walk the property and look

These build over weeks or months. Do this walk after a wet season, and again if anything on the list changes.

In the ground. New cracks in soil, paving or driveway. Bulges at the bottom of the slope. Small steps or scarps where the ground used to run smooth. Anywhere the earth appears to have pulled apart.

On the house. Doors and windows that begin to stick or stop latching. Cracks in floors, foundations or plaster that were not there last year, or that are widening. Floors that have gone out of level.

On the attachments. Decks, porches, patios or steps tilting or moving away from the main structure. This one matters: houses settle as a unit, but a moving slope pulls the lighter attachment away from the heavier building.

On anything vertical. Fence posts, utility poles, trees and retaining walls leaning where they used to stand straight. Trees curved at the base and straight above it are a classic indicator of ground that has crept.

In the utilities. Buried pipes or cables that break repeatedly in the same area. A leaking supply pipe can also be a cause, not just a symptom, so it is worth fixing quickly either way.

In the water. New springs or seeps. Ground that stays saturated where it never used to. Water appearing at the base of a slope after rain that never produced it before.

The fast signs: this is not an inspection any more

These mean the movement is under way or imminent. The correct response is to leave, uphill or sideways out of the path, not to investigate.

• A stream or channel turns suddenly muddy, or its level jumps.
• A stream drops suddenly while it is still raining. Something upstream is holding the water back, and it will not hold.
• A rumbling sound that grows louder. Often described as a freight train.
• Trees cracking, boulders knocking together, fences or poles going down in sequence uphill of you.
• The ground tilts, or you feel a jolt or vibration on a slope during heavy rain.

What to do with what you find

1. Document it. Photograph each sign with a fixed reference — a ruler, a coin, a mark on a wall — and repeat monthly. Growth over time is the evidence that matters.
2. Report it to your local authority or emergency management office. Slopes cross property lines, and so does the response.
3. Tell the neighbours. Movement rarely stops at a fence, and they may have seen the earlier stages of it.
4. Get a geotechnical assessment before spending money on repairs. Patching the cracks in a house on a moving slope buys nothing.
5. Fix the water first. Leaking pipes, blocked drains and downspouts discharging onto the slope are common, cheap-to-fix aggravating causes.
6. Pack the bag and agree the exit while the signs are still slow. Sideways out of the path, uphill, never downhill ahead of the material.

What not to do

Do not divert your water onto a neighbouring slope, do not cut into the toe of a slope to gain space, and do not add fill or a heavy structure at the top of one. All three are routine ways that a stable hillside becomes an unstable one.

The ZonaProtec monitor shows official landslide and debris-flow warnings where the local agency issues them, alongside the rest of the threats near a point you search.