Waterfalls

Four different waterfalls will then be located and investigated: Niagara Falls on the American/Canadian border in North America; Angel Falls in Venezuela, South America and High Force and Gaping Gill in Yorkshire, England.

Use the PowerPoint presentation in conjunction with the Lesson Plan. The PowerPoint presentation follows the sequence of the lesson and contains the photographs and images that illustrate the main teaching points. The Factsheet, to accompany this lesson also explains some of the main points in more detail.

Key Questions 

In what course are waterfalls a feature?

How are waterfalls formed? What physical processes are involved in their formation?

What features are characteristic of waterfalls?

How do humans use waterfalls? (With an emphasis on tourism and hydro-electric power).

Which waterfalls have global significance? (Angel Falls in South America- the highest waterfall in the world, Niagara Falls in North America- which attracts 12 million tourists every year).

Which waterfalls are significant in the UK? (Gaping Gill the highest in England and High Force- with significant gorge development).

Starter

Begin the lesson by sharing with pupils Annie Edson Taylor’s remarks: “Nobody ought ever to try that again.”

Ask pupils who could have said this and what feat should nobody ever try again? Then show pupils the photograph of Annie Edson Taylor, standing next to her barrel, during her 1901 attempt at riding over Niagara Falls. Tell pupils Annie’s story (see the Factsheet). Explain that waterfalls have fascinated people for centuries. At 57 metres, Niagara Falls are not the highest falls in the world, in fact there are more than 200 waterfalls that are higher than Niagara, but they are some of the most spectacular- due to the amount of water that plunges from them. (The highest is Angel Falls in Venzuela, South America at 979 metres).

Main Activity

Niagara Falls: Locate Niagara Falls on Google Earth, or use an atlas. The maps on the PowerPoint also locate the Falls. Explain that the Niagara Falls are located on the Niagara River, which drains Lake Erie (USA) into Lake Ontario (Canada). The Niagara River is 58km in length.

The Niagara Falls are three waterfalls that mark the border of Canada and the United States of America: 
• The Horseshoe Falls, Canada. 
• The American Falls, USA
• The Bridal Veil Falls, USA

The Horseshoe Falls is the widest and the Bridal Veil Falls the narrowest, of the three falls. The Falls are approximately 57m high.

Explain that the rapids above the Niagara Falls reach a maximum speed of 40 km per hour, but as the water flows over the overhang, it plunges at 109km per hour- the speed of a car on the motorway. 
Every second, 2,800 cubic metres of water flow over the falls. If possible, show pupils what one metre3 looks like.

Niagara Falls is eroding the landscape- every year the Falls retreat 30cm south towards Lake Erie.

Ask pupils how people interact with the physical landscape of Niagara Falls.

Tourism: Twelve million tourists visit Niagara Falls every year. Maid of the Mist boat tours are regularly scheduled. Indeed Niagara Falls is billed as a ‘vacation paradise’. Alongside boat tours, there are hotels, restaurants, various theme parks, casinos and other tourist attractions in addition to the waterfalls themselves.

Ask pupils why tourists in the winter months do not see as much water falling over the Falls as tourists visiting in summer. (Less water is diverted for use in the hydro-electric power plants in the summer months in order to give tourists a more spectacular show).

Hydro-electric power: The water from the Niagara River is used by over one million people in USA and Canada. Some of the water is used for drinking. However, much of the water is used to produce hydro-electric power.  Ask pupils what the advantages of hydro-electric power are. (HEP does not produce greenhouse gases and, once constructed, provides relatively cheap power. With Niagara Falls specifically, diverting water has helped to slow down the rate of erosion). What could the disadvantages be? The photograph on the PowerPoint shows the Sir Adam Beck Station in Canada.

Angel Falls: The Angel Falls is the highest waterfall in the world, falling 979 metres from the flat-topped Devils Mountain. It is located in south east Venezuela. The falls were named after James Angel, an American adventurer who, in 1939, crash-landed his plane nearby.

In contrast to Niagara Falls, the Angel Falls are inaccessible. To see the Angel Falls, requires a plane journey into the Canaima National Park, followed by a four hour boat trip along the Churun River and finally an hour’s hike through dense forest.

Under certain conditions, a visitor can feel small water drops from one km away. 

So how are waterfalls formed?

The formation of waterfalls: Ask pupils in which part are a river are waterfalls located? They should know this from Lesson One. (Waterfalls are formed in the upper course where the land is steep, rather than the middle and lower courses where the land is flatter)

What are the characteristics of the landscape in the upper course? (Steep/high elevation)

Show pupils the diagram of a cross section of a waterfall as you explain how they are formed.

Waterfalls are formed as the river flows downstream. The river can flow over different rocks- some are hard and some are softer. As water flows it erodes the rocks. However, it erodes layers of softer rock more quickly and easily than the layers (or strata) of harder rock.

In the diagram you can see that a strata of hard rock is on top of soft rock.

As the water flows over the waterfall the softer rock will be undercut- exposing the strata of hard rock which will begin to overhang the softer rock beneath it. Over time, the overhanging hard rock will collapse.

The process then continues, with soft rock eroding and hard rock collapsing. This results in the waterfall moving, or retreating upstream, carving a steep gorge into the landscape as it does. A plunge pool is created at the base of waterfalls. The water is very turbulent here, and combined with the fallen rocks, acts to erode a deep hole, or pool in the river bed.

Ridges of hard and soft rock can also create an uneven river bed, which generates rapids.

The gorge cut by the retreat of the Niagara Falls is 11km long. More modestly, High Force waterfall on the River Tees in Yorkshire retreats at a rate of 5-6mm per year and has a gorge 700 metres long.

England’s highest waterfall: Gaping Gill waterfall is located on the river Fell Beck, North Yorkshire and has a drop of 98 metres. However, it cannot be seen from the surface, because the waterfall plunges below ground into a pothole. However, pothole clubs hold regular ‘winch meets’ to allow tourists to be winched down into the deep cavern to see the waterfall for themselves. Use Google Earth to locate the entrance of the pothole.

There are a choice of activities that teachers can tailor to suit the needs of their own pupils. 

A waterfall flip-book: Pupils can create a waterfall flip-book. The waterfall can be drawn in cross section. Initially the pages will show how the waterfall flows. Then, the flip-book can show how the waterfall undercuts the soft rock strata eventually leading to the collapse of the overhanging hard rock. The waterfall can then retreat, leaving behind a steep sided gorge. This activity is suitable for pupils who are very able artists. For schools with access to cameras or iPads, this activity could be tailored to the production  waterfall stop-go animation.

A waterfall model: Pupils can make a model of the cross section of a waterfall in plasticine. It is best to use a disposable plastic container to house the model and lend it structure and stability. Use several different colours of plasticine to represent the different rock strata, the river banks and the water itself. High ability pupils should be expected to add extra detail to their models, for example by incorporating the plunge pool. They may also write labels for each feature, securing them with cocktail sticks. This activity is suitable for pupils of all abilities, and works well for pupils in small groups.

Plenary

Pupils can play the game ‘Just a Minute’. 

Choose a confident pupil to begin. Can they speak for one minute without hesitation, repetition or deviation (and using factual information and correct vocabulary) on the topic of Rivers?

Time the pupil and see how long they can speak. The class teacher can ‘buzz’ the pupil out if they ‘um and ah’, repeat themselves or are factually incorrect. Alternatively, other pupils can ‘buzz’ by a show of hands, or other device, as long as they have a good reason.

Does the class have a ‘Just a Minute’ champion?