The thunderstorm, the flood and the landslide

Ben Dolphin

Generally speaking, we in Scotland live in a quiet corner of the world. Our volcanoes are long extinct and there’s not been a major landscaping event since the glacial ice retreated. Sure, the earth shakes from time to time, and the turbulent atmosphere occasionally rattles our homes, but for the most part we live on pretty solid ground. We can therefore be forgiven for looking at our landscapes with a comforting sense of permanence. This is how it has always been, and this is how it will always be. Scotland is timeless. Scotland is forever.

It’s an illusion of course, because nothing in the natural world is ever finished in that sense. It doesn’t matter how quiet our earthly neighbourhood might seem, we occupy a dynamic system that is constantly building, destroying and recycling. Every second of every day, weathering and erosion are whittling our timeless landscapes down and carrying them away.

For the most part, this happens so infinitesimally slowly that we’re barely able to perceive it. But every now and then, the brakes get released and we are rudely reminded just how impermanent our permanence is. August 11th 2020 was one such day.

That evening, a line of convection formed over eastern Scotland and kicked-off what was, for many people, the longest and most intense thunderstorm they’d ever experienced. They’re rare occurrences in Fife at the best of times – they don’t last long, offer up barely a dozen flashes of lightning, and they hardly ever happen at night – but this one clearly hadn’t read the script.

Snapped from the front door!

As soon as I heard the first ominous rumble I opened the front door to inhale the approaching storm. I expected to be stood there for just 15 or 20 minutes and then return to the sofa, but five hours later I hadn’t moved from that spot. It just didn’t let up, the power of the thing so mesmerising that I couldn’t tear myself away. And let’s be honest, nothing on telly can match a thunderstorm!

Much of east-central Scotland and Aberdeenshire was hit at some point, but here in the Lomond Hills it kicked off at 8pm and went on till around 1am, before pepping up again around dawn. More than 20,000 lightning strikes hit eastern Scotland that night and it genuinely felt like I saw every single one.

I’ve certainly never seen a light show like it, but it was the rainfall that made the headlines the next day. Dunottar in Aberdeenshire took the record for the most rain recorded in a single hour, at almost 60mm, but most places had a month’s rainfall or more in just three hours. Fife Airport (yes, Fife has an airport!) near Glenrothes recorded 105.6mm from the storm, which is more than four inches. The Fife average for the whole of August is just 70mm!

Unsurprisingly there was widespread flash flooding, and a major incident was declared in Fife after cars started floating past Kirkcaldy’s Victoria Hospital, and static caravans slid down the hillside at Kinghorn. Elsewhere, 30 metres of the Union Canal in Falkirk gave way and released its water onto the Glasgow-Edinburgh railway. And sadly, a landslide was believed to have caused the derailment of a train near Stonehaven, in which three people died.

But the full impacts of that one storm upon my local landscape only slowly revealed themselves to me over the subsequent weeks and months. I kept encountering odd sights, incongruous in their environments – large rocks marooned on tracks, paths surfaces washed away, snapped branches half way up trees, muddy smears down hillsides. Small things in themselves, but together forming a bigger picture of a significant and unusually widespread event.

Photo No.2 caption: Top: boulders washed off a wall and onto the path. Bottom: slides in Glenvale (spot the walkers!)

The most curious damage I encountered was during a wonderfully rugged walk along the Water of May in the Ochils where, in the middle of a spruce plantation, the sturdy green riverbank I’d been following gradually liquefied under my feet before morphing into a large area of shingle. The natural course of the river seemed to veer to the right of the shingle, but a greater portion of the Water of May was instead running away to my left, straight over the shingle and into the trees.

What was formerly a dry spruce plantation was now a peculiar mossy green swamp. A thick layer of stones, silt and broken branches covered the forest floor, over which a shallow but broad flow of water was now running. I followed it through the woodland and soon found the flow being channelled towards a pretty wee waterfall, at which point it rejoined the rest of the Water of May. Said waterfall had clearly once been the dry riverbank, the greenness of the vegetation at the bottom of the water clearly indicating this was a recent diversion, and the August storm was the only suspect in the room.

It’s not unusual for rivers to bend and flex over time, of course. That’s just what they do. For the most part it’s a slow process but what this event at the Water of May rammed home to me was just how quickly things can change. Rivers can re-route suddenly when an existing barrier gives way, or when a new one is created. It was possibly both in this instance, a substantial flood surge perhaps coming down the river and breaking through the bank, whilst simultaneously depositing a large enough volume of stone to create a barrier that also split the river in two.

The re-routing of the Water of May

The upshot of this diversion is that the inundated spruce trees will die and fall over. Habitats will perish, but in so doing they will create new ones. The resulting dead wood will become home to many new species, and calmer pools will be created behind the fallen logs.

Erosion along the river will however hasten, as the dry land between the two channels gets eaten away on two fronts rather than just one. Rocks become stones become sediment. And steadily, particle by particle, the ground below our feet is carried away downstream and out to sea.

Elsewhere, the most shocking impact of the storm (to me at least, as a local) occurred just a couple of miles from my home, although I didn’t actually become aware of it till six months after the event.

A local geomorphologist contacted me in February this year to ask if I had any reliable rainfall data for the storm, given my proximity to ‘the landslide, the biggest one’. I had no idea what she was talking about until she sent photos through, and I was duly astonished. A landslide had decimated a section of the forest on the Falkland Estate.

By the time I paid the site a visit, only a few weeks ago, the raw scar of the destruction zone had obviously softened somewhat. For starters, the estate has done an amazing job clearing the debris from the forest roads and digging new drainage ditches, but new growth of green vegetation has also taken hold. It’s amazing how quickly nature is able to paint over the blemishes, but even so, less than a year after the event there was still no hiding it, and I was taken aback at its scale.

Landslides aren’t uncommon in Scotland. I mean, just look at how many times the Rest and be Thankful has been closed in the last couple of decades! But in this neck of the woods, in the drier east, we have lesser extremes of weather and fewer steep slopes, so large destructive slides are rare.

The landslide’s terminal point wasn’t hard to find, as there was a wide area of mud, rocks, logs and branches where it had finally run out of steam at the forest edge. I slowly followed the destruction ‘upstream’, taking it all in, first crossing a forest road (long since ploughed clear) and then following a deep sandy fissure that looked like two tectonic plates were pulling apart. The fissure got wider and deeper the further upstream I went, the power of the water laid bare by the deep cut into sandy soil.

Falkland floodwater cuts a flippin’ great big trench!

Numerous large boulders had originally been left scattered about the forest, but they’ve since been incorporated into the road repairs and reinforcement works. One remained, however, surreally perched above the trench with a dead tree jammed horizontally on top. A sobering thought, picturing objects as big as that tumbling through this normally benign and comforting place.

Continuing up through the forest, a brown v-shaped trench of mud, rock and sand cut its way through steeper ground, and as it did so the scene got steadily more apocalyptic. Larch were leaning or scattered at haphazard angles, splintered and broken, while any trees left standing at the edge of the slide were stripped of their bark or splattered with mud more than 6ft up the trunks.

The ground beneath my feet was clearly still very unstable so I left the channel and steered a broad arc away from it, working my way through the forest towards the upper reaches of the slide. To my surprise there wasn’t just one starting point. Several areas of the slope had failed on either side of a gully, right down to the bedrock, leaving a collection of pale sandy tongues reaching up the steep wooded hillside.

An apocalyptic aftermath

The cause was of course a phenomenal amount of rain having fallen. That, in itself, isn’t necessarily a problem if it falls over a longer period of time and is able to drain away without compromising the slope. But when that much rain falls in a short space of time, it can alter the delicate balance between the forces that restrict movement of material, and those that drive it.

Friction for example, can prevent a hillside slipping downwards. But when that hillside becomes saturated it not only becomes much heavier, which gravity obviously delights in, but it also acts as a lubricant. And what might begin its journey downhill as a rocky mess can quickly become more like liquid as the slide churns up with the water and becomes more of a flow.

To my untrained eye, from its beginnings at the top of the escarpment the landslide appeared to have rushed steeply down the Forthear Burn some 160m to the forest road, beyond which it surged for at least another 300m across flatter ground. In all, almost half a kilometre from top to bottom. But I’m no geomorphologist, and it’s since been pointed out to me that the distance between the uppermost slope failure and the farthest flung debris in the forest is more like 1km!

Clockwise from top left: the solitary boulder; upper reaches of the Falkland slide; one of many slope failures; debris surged through the forest

Impressive in itself, but that wasn’t the only landslide that night. There were numerous other slides along that 5km escarpment, most of them on a smaller scale but nonetheless managing to surge across paths and tracks. It was as though someone had pressed ‘fast forward’ at a landscape scale and sped through decades of erosion in just a few hours. And that did make me feel quite sad, to be honest.

I’ve seen plenty of erosion scars on hillsides elsewhere, and lord knows the Lomond escarpment is littered with chutes of debris from dozens of ancient slides, but it still cuts in an oddly personal way to see your local hills succumb so dramatically. I know it’s all part of the process, part of the plan, and I know that these are dynamic environments that should be allowed to act naturally, but it’s still quite discomforting to see how easily…..and quickly…..cherished places can be whittled away.

Still, it must have been a truly awesome thing to behold, seeing and hearing the landscape move like that. Trees snapping and crashing, boulders thundering downhill. But as I walked home after my site visit, occasionally passing below yet another exposed slab of bedrock, those familiar slopes now unnerved me in a way they’ve never done before. What was formerly completely benign was now oddly menacing, as I got the sense that anywhere in the Lomond Hills could easily have slid that night.

As a result, my confidence in the Lomond sandstone I so often find myself standing on has undoubtedly been shaken, and I realise how easy it is to become complacent once the calm has returned. And return it has, because aside from the visual scars, what struck me most at both the Water of May and at Falkland was how gorgeously quiet those places now were. How incongruous the destruction was. Indeed while I was standing examining the solitary boulder, a red squirrel scurried out onto a nearby branch and sat eating a pine cone, just metres from me. Relaxed and preoccupied, I could clearly hear it nibbling in the sunshine. The scene was as far a cry as you could get from the angry destructive forces of floods and landslides.

After nearly a minute the squirrel finally noticed me and dropped its pine cone in surprise. It squeaked a few times in alarm, and then disappeared up into the canopy. I stood still and listened but everything had fallen quiet. The squirrel had gone and everything was motionless, the landscape apparently frozen into place once again. Timeless, forever, permanent….until it isn’t.

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