Mauao and Pilot Bay. Photo: Alexander Klink, Creative Commons
My heart goes out to everyone impacted by weather events and landslides over this past week. The incoming news that a landslide has gone through the Mount Maunganui Beachside Holiday Park was gut-wrenching.
Mount Maunganui. Creative Commons. Schwede66
Landslides, a type of mass-wasting, can range from a nuisance to an overwhelming disaster. They can be small and barely noticed, or large enough to bury a town. Importantly, there are sometimes warning signs that the land is beginning to give way.
Janine Krippner
If we notice and understand these warning signs, it could give precious time to get out of the way. This is not at all to say that there were any warning signs before the current event that should have been noticed. I have no information beyond the initial news, and I will not be speculating.
What we can do is remind ourselves about what those signs are, just in case.
Landslides are not always a single mass of land sliding downhill. They can occur in multiple steps over time. Land can move under the constant force of gravity, with or without a clear trigger like a severe weather event or an earthquake.
When there is warning, what might we see?
Websites from organisations like the USGS and our own Civil Defence agencies have more extensive information pages with helpful photos. What follows is a summary.
When rock and soil start to creep downhill, the ground deforms or changes. Outside, this can look like cracks forming in the soil or anything on or within it, like roads, paths, retaining walls, fences, or other structures. Bricks in a building might begin to pull apart.
There may also be bulging in the ground, or water ponding in places where it had not before. Trees, power poles, or streetlamps might tilt, and power lines might sag or become taught. Buried utility lines, such as water or sewage, might break or begin leaking.
If you are near a stream or river there may be a rapid change in water level.
Inside, warning signs can include new gaps appearing, or doors and windows sticking or not fitting as they once did. Decks, verandahs, or steps might start to tilt away from the building.
As people near the Mount Maunganui event have described, once a landslide gets moving it can be loud, and shaking may be felt. This can include boulders crashing together, a deep rumble or ground vibrations (often described as sounding like a freight train), or the sound of snapping wood or other materials being impacted.
It is important to remember that landslides can occur in several stages. When the first movement stops, it does not necessarily mean the area is safe. Landslide scars can continue to collapse over time, retreating further into a hillside or cliff.
Landslides can move incredibly fast, so immediate action like evacuation is critical.
There may be no perceivable warning signs at all. But when there are, noticing them can make a real difference. Once safe, contact your local council or emergency services and let the right people know.
Mauao and Pilot Bay. Photo: Alexander Klink, Creative Commons
