5.8 — Landslide and Avalanche

Both give warning signs, both are frequently missed, and both are far more common than people think in the places where they occur.

Landslide

When they happen

Overwhelmingly during or shortly after prolonged or intense rainfall (5.4).

Also after earthquakes, after wildfires — because the vegetation holding the soil has burned — during rapid snowmelt, and following construction that has cut into a slope or loaded the top of one.

And the highest-risk period in a monsoon region is not the heaviest day. It is after several days of accumulated rain, when the ground is saturated and the slope has lost its friction.

The warning signs

And these are the most valuable thing in the chapter, because they are visible days or hours in advance and almost nobody knows them.

In the ground:

New cracks appearing in the ground, in paths, or in a road surface.

Ground bulging at the base of a slope.

New springs, seeps, or wet ground where it has always been dry.

Water that suddenly runs muddy when it was clear — this indicates soil movement upstream and it is one of the strongest signs.

Or a stream that suddenly runs clear when it was muddy, or stops flowing, which can indicate that it has been dammed by a slip upstream — and that the dam will fail.

In structures:

New cracks in walls, particularly diagonal ones.

Doors and windows that begin to jam.

Floors or steps separating from walls.

Fences, poles, walls or trees tilting or moving.

And broken utility lines.

And sound:

**A rumbling that grows louder. **Trees cracking. Boulders knocking.

Any of these during heavy rain in a hilly area: leave immediately.

What to do

If you see the signs: get out of the path.

Move perpendicular to the slope, sideways, out of the likely flow line — not down the valley, which is where it is going.

Get to high ground on the side.

Alert your neighbours as you go.

And if you cannot escape: curl into a tight ball and protect your head. It is the last resort and it does improve outcomes.

At night

The most dangerous time, because the signs are not visible.

During heavy prolonged rain in a landslide-prone area, the correct action is to relocate before dark rather than to sleep and monitor.

A very large proportion of landslide deaths occur to people asleep.

Driving

Watch for collapsed road surfaces, fallen rocks, and mud on the road.

And do not drive through or over debris flows — they are moving and they are far deeper than they look.

Before

Know whether your slope is at risk. Hazard maps exist; a long-term local resident knows.

Do not build at the top or bottom of a steep slope, or cut into one, without engineering advice.

Watch for changes after any nearby construction, which is a common trigger.

And plant vegetation on slopes. Roots hold soil, and stripped slopes fail.

Avalanche

Relevant to anybody in snow-covered mountains, and the numbers are worth knowing because they explain the urgency.

The survival curve

Survival for a completely buried person is high in the first minutes — roughly ninety per cent in the first fifteen minutes or so — and falls very steeply after that.

Which means: rescue is done by the people who are there. Organised rescue almost always arrives too late for a burial.

And that single fact determines everything about avalanche safety.

The equipment

Three items, and they are only useful together, and only if everybody in the group has them and knows how to use them.

A transceiver — worn, switched on, in send mode.

A probe — to locate precisely once the transceiver has given the area.

And a shovel — because digging a person out of avalanche debris, which sets hard, is not possible by hand.

Carrying them without practising is close to useless. The search has to be fast and it is a skill.

An avalanche airbag, if you have one, substantially improves the chance of staying near the surface.

The conditions

Most avalanches are triggered by the victim or their group.

High-risk indicators: recent heavy snowfall, particularly in the last twenty-four to forty-eight hours; strong wind loading snow onto lee slopes; rapid warming; a weak layer in the snowpack; and recent avalanche activity visible nearby.

Slope angle matters enormously: most slab avalanches release on slopes of roughly 30 to 45 degrees.

And check the local avalanche forecast. They exist in most mountain regions, they are good, and they are free.

If you are caught

Try to move to the side, out of the flow.

Get rid of poles and skis if you can.

Swim, aggressively, towards the surface.

As it slows, thrust one arm upward — a visible hand dramatically speeds location.

And critically: create an air pocket in front of your face with your other arm, before the snow stops moving. Once it stops it sets like concrete and you cannot move at all. The air pocket is what buys the minutes.

Then stay calm and conserve air.

If somebody else is caught

Watch them. **Mark the point where they went in and the point where you last saw them. These two points define the search line.

Search immediately. Do not go for help first — the survival curve means that going for help is usually going for a recovery.

Switch transceivers to search, probe, dig.

And dig from the downhill side, in from the side rather than straight down.

The common lesson

Both hazards are read by people who know the signs and missed by people who do not — and the signs are learnable in ten minutes.

And in both, the people who survive are rescued by whoever was already there.

What to do with this page

Muddy water where it was clear, new cracks, jamming doors, tilting poles. Any of these during heavy rain on a slope: leave.

Move sideways out of the flow line, not downhill.

Relocate before dark during prolonged rain in a landslide area.

Avalanche: transceiver, probe, shovel — all three, practised, or they are decoration.

And make the air pocket before the snow stops moving. After that you cannot move at all.

Next: 5.9 — wildfire, where the decision to leave has to be made much earlier than instinct suggests.