It is a good idea to try to park your car in the shade. Usually. But it can also be a good idea to take some account of the weather conditions and the type and size of trees you are parking under.
Acacia trees – such icons of Kenya’s global image – normally prompt caution because of the probability of tyre punctures from the thorns under their canopy. But when they are very large and very old, it is not only your tyres they might flatten.
That was the ‘being-wise-after-the-event’ thinking near the shores of Lake Naivasha last week, (I was there when it happened, if you’re wondering) when a freak gust of wind hit one of the biggest acacias you will ever see – more than 30 metres tall, a canopy span to match, and a trunk diameter of nearly two metres at the base. Even its upper branches were 50cm thick, and its overall weight was several thousand kilos. It must have been growing for at least half-a-century to achieve those dimensions, and that’s getting towards the best-by date for that species.
On the day this magnificent giant finally keeled over, without forewarning of any kind and in a freak gust of wind, there were a couple of dozen cars in a nearby parking area and perhaps 100 people in the adjacent restaurant having lunch under initially clear blue skies. None of the cars was apparently “under” the tree, which was quite far away in the middle of a lawn.
Rainstorm
Not, it transpired, far enough away, as the sky quickly darkened and thundered and a rainstorm swept across the water with a leading edge of blustery wind and light but stinging rain. Some of the diners scuttled out to their cars to get warmer clothes. All but one were back at their tables when a particularly fierce twist of wind whipped through the shoreline woodland.
The giant started to tumble, its shallow roots ripping up through the sodden earth already softened by recent rains. As it fell, it touched another large acacia, but with such acceleration and weight it snapped the other’s trunk as if it were a twig, with a cannon-shot of noise that turned every head in the place.
The mighty acacia that caused the damage. It was more than 30 metres tall.
The main trunk of the colossus fell groundwards without touching anything else, but its central branches (themselves as thick as normal tree trunks) and its upper structure reached a line of half a dozen cars, diagonally.
The fickle finger of fate
The force generated by a 30-metre lever weighing several tons and accelerated by the force of gravity (10 metres per second per second, sic) was astonishing. And it was delivered with the usual message of how fickle fate can be.
The parking place chosen by each car was largely a matter of chance. None, I suspect, picked their spot in case a big tree fell over. They certainly did not compute where each branch might fall. A shadier spot was a win, not a risk.
Yet, in destinies chosen by a breeze, some escaped unscathed, others suffered minor blows from fragile branches or by bigger branches shaping like domes above their roofs, while others took the full force of the fall from the stoutest branches at the heaviest fall points. Four vehicles suffered the brunt of the impact. Nevertheless, it remains good advice to always try to park your vehicle in the shade, with a little extra circumspection in very wet or windy seasons.
The root of the problem
Acacias (particularly the Xanthophloea or Fever Trees) are especially prone to suddenly falling over for two reasons. First, they have a relatively short lifespan of around 50 years, so a high proportion of the big ones are ‘old’. Many other species of tree can live 10 times that long…or more, so the majority are in their prime.
Second, their fast growth and survival strategy in poor soils is to develop long lateral roots, optimising both nutrient and surface water availability in shallow top-soil. They are therefore not underpinned/stabilised by a deep central tap root. In windy conditions (like many forest trees) they rely on their neighbours to share the strain.
Some of the vehicles that were damaged after fierce winds uprooted a tree that fell on parked vehicles at Carnelleys Hotel on the shores of Lake Naivasha.
They also have a unique trick – they are the only tree whose bark can photosynthesise (like a leaf), and the bark can grow back over a branch of bare and dead wood (for instance after a fire) and continue to grow afresh beyond the dead core. Over time the new branch can become too heavy for the brittle deadwood inside.
Signs that any tree is nearing the end of its time – or is in the process of dying for any other reason like disease, damage or starvation – include leafless branches, peeling bark, falling branches, cracks in the trunk, bracket fungi or high infestation with insects (to whom dead wood is both food and a dream home).
And, of course, if the tree is starting to lean over and drag its roots into a bulge at the base of the trunk. There is a chance that any such tree has been at least partly hollowed out at its centre, and lacks the strength to reliably support its own weight. If you suspect a tree may be ‘in trouble’ in any of these way and its location would do serious damage if it fell (in whole or in part) call an arborist.
Anyway, three of the cars felt the fullest force. The largest branch to hit the ground, even before the main trunk fully landed, crushed the rear corner of the large bronze 4WD estate that I had travelled to Naivasha in, though I was a passenger, (See it on the cover of this magazine), pulling the roof down to the load bed and completely demolishing its reinforced tailgate. This collapse of a purposively built “crumple zone” absorbed some of the energy before the branch hit the next car (silver saloon) which had the misfortune to be hit at a heavy fork in the branch… The right-hand arm of that fork first hit the middle of the car’s roof…still so hard that the roof (though part of the reinforced passenger safety cell) was crushed below the level of the seat backs. That soaked up more energy and the remaining force of the left-hand fork hit the rear of the roof of the metallic grey 4WD estate, which absorbed most of the remaining energy. That’s why the silver saloon’s boot suffered less damage. The metallic grey vehicle also had a subsidiary branch land across its bonnet. Its full static weight squashed the suspension to its limit, but did not have the kinetic force to pulverize the bodywork.
It is encouraging to note that although the cargo section was totally distorted, the reinforced passenger safety cell (the front half of the roof above the side doors and seats, where I had been sitting as a passenger when we arrived) remained substantially in shape, even despite a side force that pulled the door pillar away from the back door. While much of the vehicle, from the classy Goodrich tyres to the entire front end appeared undamaged, this is probably a borderline case between a long and expensive repair and a write-off.
A nearly new green 4WD pick-up was hit by double branches directly on the front of its cab and windscreen with a force no safety cell is designed to withstand. Although the rest of the vehicle was superficially unscathed, there is a distinct possibility that the lateral force of the blow bent the whole length of the vehicle amidships. A new cab is one thing, a bent chassis is another. Though the damage is probably repairable, it was a good time not to be in the driver’s seat.
The main tree trunk with people and vehicles in background (see main picture)
The main trunk had a diameter of about 2 metres. The severe splitting at the top of the bole illustrates the force (weight multiplied by speed) with which the leading big branches hit the ground.
The tree did not snap – it simply keeled over, ripping up its shallow roots and a ton of topsoil.
Cars struck by lighter branches suffered only minor damage. The branch across the windscreen of a black SUV did not improve the wiper blades, but landed gently enough not to break the windscreen. The equally thin branch across the roof lay on top with enough pressure to compress the rear suspension, and had to be cut before the car could be driven away.
The crushed roof of the silver saloon, above
The damage to this car was so severe that probably no single panel on any of the vehicle was unbent, and that includes the floorpan. Many other components, seen and unseen, could also have been distorted or weakened.
This is an unequivocal write-off, and in many parts of the world, any attempt to repair or even salvage parts would be forbidden on safety grounds. This vehicle’s final journey would be to a crushing plant.
What a day that was… BY DAILY NATION