Waterfalls are one of those features of the landscape that are hard not to stop and look at. Whether it is a huge waterfall surrounded by dramatic cliffs or a small waterfall hidden away in a woodland, there is something about watching water make its way over rocks and drop through the landscape that makes you want to explore further.
But what actually makes a waterfall a waterfall?
How are they formed? Why do some have one huge drop while others tumble down a series of rocky steps? And when you see a waterfall described as being a certain height, how is that height actually measured?
There is quite a lot more to waterfalls than simply water falling over a cliff.
In this guide, I’ll take a look at what waterfalls are, how they form, the different types you might come across, how they are measured and why they are constantly changing.
What Is A Waterfall?
Put simply, a waterfall is a section of a river or stream where water flows over a steep drop or series of drops in the landscape.
That sounds fairly straightforward, but there isn’t actually one universally agreed definition of exactly what counts as a waterfall.
Some waterfalls are huge and instantly recognisable, while others are much smaller and sit somewhere between a waterfall and a cascade. There are also places where a river flows quickly over a steep, rocky section without having one obvious drop, which can make it difficult to decide whether you’re looking at a waterfall, a cascade or simply a rapid.
This is why you may sometimes find different descriptions of the same feature depending on where you look.
For me, though, I don’t think a waterfall has to be enormous to be worth visiting. Some of the smaller waterfalls I’ve visited, like Ffynone have been just as enjoyable to discover as the much bigger ones.
How Are Waterfalls Formed?
Waterfalls are generally formed through a combination of flowing water, erosion, geology and the shape of the landscape.
One of the most common ways a waterfall forms is where a river or stream flows over different types of rock that don’t erode at the same rate.
Harder, more resistant rock can withstand erosion for longer, while softer rock is gradually worn away by the flowing water. Over a very long period of time, this difference in erosion can create a steep drop in the river.
You can see examples of this at some of the waterfalls around the UK, such as at Hayburn Wyke Beach, where the water has gradually worked its way through layers of rock and shaped the landscape around it.
As the water continues to flow over the edge, erosion can also take place at the base of the waterfall. Falling water and sediment carried by the river can gradually wear away the rock beneath the falls, creating or deepening a plunge pool.
The rock behind the waterfall can also become undercut as softer material is eroded away. Eventually, the harder rock above can become unstable and sections can collapse.
When this happens repeatedly over a very long period of time, the waterfall can gradually retreat upstream.
This process happens incredibly slowly. We’re talking about geological timescales, often thousands or millions of years, rather than something you’re going to notice during a normal visit.
But it means that waterfalls aren’t actually fixed features of the landscape. They are constantly being shaped and changed by the water, rock and landscape around them.
How Does A Waterfall Change Over Time?
Once a waterfall has formed, the process doesn’t stop.
Water continues to interact with the rock and gradually alters the shape of the riverbed.
Erosion at the base of a waterfall can deepen a plunge pool, while erosion around the rock behind the falls can gradually weaken the area supporting the waterfall’s edge.
Eventually, sections of rock can collapse.
When this happens repeatedly over a very long period, the waterfall can gradually retreat upstream.
This means that the position and shape of a waterfall aren’t necessarily fixed forever.
The landscape around it changes too. Rivers can carve deeper channels, plunge pools can become larger and rocks can break away from surrounding cliffs and gorge walls.
So although a waterfall can look like a completely permanent part of the landscape when you stand in front of it, you’re really looking at one point in a much longer geological story.
What Are The Different Types of Waterfalls?
Not all waterfalls look the same.
Some have one dramatic vertical drop, while others tumble down a series of rocky steps. Some are wide and spread out, while others are narrow and plunge into a pool below.
There are several different terms used to describe waterfall types, although the terminology isn’t always completely consistent.
Here are some of the main types you are likely to come across.
Plunge waterfalls
A plunge waterfall is where the water drops vertically from the top of the waterfall, often with little or no contact with the rock face as it falls.
These are probably the type of waterfall most people picture when they hear the word “waterfall”.
If the water flow is strong enough, the falling water can appear to separate completely from the cliff before reaching the pool below.
Cascade waterfalls
A cascade is where water flows down a series of smaller rocky steps or a steep slope rather than making one single vertical drop.
Cascades are particularly common in rocky and mountainous areas.
Some can be relatively short, while others can continue for a considerable distance.
The distinction between a cascade and a waterfall isn’t always clear, which is why you may see the same feature described differently by different sources.
Tiered waterfalls
A tiered waterfall consists of several distinct drops, with sections of river flowing between them.
Some tiered waterfalls have two or three obvious drops, while others can contain many more.
This can sometimes make it difficult to decide how tall a waterfall actually is, because you have to decide whether you are measuring the largest individual drop or the total vertical drop across all the tiers.
Horsetail waterfalls
A horsetail waterfall is where the water remains in contact with the rock face as it falls, rather than dropping completely away from it. The water typically spreads out as it descends, creating a shape that can resemble a horse’s tail.
Grey Mare’s Tail is a great example of this type of waterfall, with the water flowing down the steep rock face rather than making one single vertical drop.
Fan waterfalls
Fan waterfalls spread out as they descend, becoming wider towards the bottom.
The shape of the rock and the way the water flows over the edge can create a broad, fan-like appearance.
Block waterfalls
Block waterfalls are generally wider waterfalls where water flows over a relatively broad, fairly straight edge, creating a wide sheet of falling water. They can look particularly impressive when the river is carrying a larger volume of water.
Cwmfelin Waterfall is a good example of this type, with the water spreading across the rocky edge before dropping over the falls.
Can A Waterfall Be More Than One Type?
Yes.
This is another reason waterfall terminology can sometimes be confusing.
A waterfall can have characteristics of more than one type, particularly when it has several different sections.
For example, a waterfall might begin with a vertical plunge before continuing as a cascade further downstream.
A tiered waterfall might also contain individual plunge sections and cascades between its main drops.
So the different categories are useful for describing what a waterfall looks like, but they aren’t necessarily rigid boxes that every waterfall fits neatly into.
If you’re looking for new waterfalls to explore, take a look at my How to Find Waterfalls in the UK guide, where I share the different ways I find new waterfalls to visit.
How Are Waterfalls Measured?
Waterfall height sounds like it should be very simple. You might think you just measure from the top of the waterfall to the bottom.
In reality, it can be much more complicated.
The problem is that not every waterfall has one obvious top and bottom. A waterfall might consist of several separate drops, a long cascade or a combination of steep sections and vertical drops. You then have to decide exactly which parts of the waterfall should be included in the measurement.
Cenarth Falls is a good example of why measuring waterfalls isn’t always as straightforward as it might seem. The falls consist of a broad, rocky section of the River Teifi rather than one simple vertical drop, so there isn’t necessarily one obvious point that everyone would choose as the top and bottom measurement points.
This is one reason why you can sometimes find different heights quoted for the same waterfall.
Total Height vs Individual Drop
Imagine a waterfall with three separate drops.
The first drop is 10 metres, the second is 15 metres and the third is another 10 metres.
The waterfall could be described as having a total vertical drop of around 35 metres, while its highest individual drop is only 15 metres.
Neither figure is necessarily wrong. They are simply measuring different things.
This becomes particularly important when waterfalls are described as being among the tallest in a particular area.
The answer can depend on whether someone is talking about the total vertical drop of the waterfall or the height of its largest individual drop.
Why Do Different Sources Give Different Heights?
There are several reasons.
Different sources may use different measurements, or they may define the top and bottom of the waterfall differently.
One person may include every section of a long cascade, while another may only measure the main drop.
There can also be practical difficulties when trying to establish a waterfall’s height, particularly when the terrain is steep or the very top or bottom is difficult to access.
For larger or more complicated waterfalls, height can be estimated using things such as topographic maps and elevation data, or measured in the field using specialist equipment.
So if you come across two different figures for the height of a waterfall, it doesn’t necessarily mean that one source is wrong.
It may simply be that they are measuring it differently or defining the waterfall differently.
What is a Seasonal Waterfall?
Some waterfalls don’t have a consistent flow throughout the year.
Their flow can depend heavily on the amount of water entering the river or stream, meaning they may be much more impressive at certain times and considerably smaller at others.
Some can even dry up completely during prolonged dry periods.
Other waterfalls are fed by more reliable rivers or springs and therefore have a much more consistent flow.
The amount of rainfall, the landscape, the size of the catchment and the geology of the area can all influence how much water eventually reaches a waterfall.
Why Are Waterfalls Important?
It is easy to look at a waterfall simply as something beautiful to visit, but waterfalls are also an important part of the natural landscape.
A waterfall is part of a river or stream, so it is connected to the wider watercourse and the landscape around it. The river provides an important source of water for plants and wildlife, while the surrounding woodland, rocks and vegetation form part of the wider ecosystem.
Waterfalls also help to shape the landscape. As we’ve seen, erosion caused by flowing water can carve out rocky channels, plunge pools, valleys and gorges over very long periods of time.
They can also have an importance to people. Waterfalls attract walkers, photographers, nature lovers and tourists, while some have interesting historical or cultural connections.
Falling Foss is a good example of how a waterfall can be part of a much wider landscape, with the falls surrounded by woodland and the River Midge flowing through the valley. The area has also had an important connection with people over the years, including the historic Falling Foss Tea Garden and the nearby Midge Hall.
The waterfalls we enjoy today are therefore part of much bigger natural and human stories.
Final Thoughts
There is a lot more to waterfalls than simply water falling over a rock.
They are shaped by geology, water and erosion, and the waterfall you see today is just one stage in a much longer story.
I think that’s part of what makes visiting them so interesting.
You can stand in front of a waterfall and see something that looks completely permanent, while underneath it all the water is still slowly shaping the rock and changing the landscape.
And no two waterfalls are quite the same.
Some are huge and dramatic, some are small and hidden away, and others are somewhere in between. Some are surrounded by mountains and rocky gorges, while others are tucked away in quiet woodland.
That’s what makes exploring them so much fun.
There are always more waterfalls to discover.
Thinking about swimming at a waterfall? I’ve put together a Wild Swimming at Waterfalls guide with some important things to consider before getting in.
