Misconceiving Physical Geography

Some misconceptions (or ‘alternative conceptions’) are a legacy of past knowledge and ways of understanding the world that are no longer valid, i.e. replaced by new ideas that make better sense of evidence (old and new). However the old ideas have such inertia that they linger in seemingly ‘authoritative’ sources (textbooks, videos or online), and in students’ minds (and perhaps some teachers also) are taken as ‘true’. Other misconceptions are due to teaching oversimplification, where the ‘model’ does not fit the reality, and ultimately clouds a student’s ability to interpret real situations (Stephen Trudgill called this ‘the tyranny of models’). And then there are the ideas that students (and perhaps some teachers also) find a challenge to grasp. Often this is not because students are not thinking intelligently about the geography; it can be that the idea being presented is counterintuitive. Frequently, students bring their ‘common-sense’ understanding of the physical world that doesn’t adequately explain or reliably reflect what happens in the real world.  Let me give an example. Some years ago I interviewed a cohort of secondary-aged students about their experiences of physical geography in school lessons.  Here, from my interviews, is Rebecca (aged 15):

“Physical geography…oh its’ easy enough to learn the diagrams and I quite like drawing them, and they are easy to do in an exam, but it doesn’t always make sense. I mean … like … low pressure for instance … you know, high pressure, low pressure … how can you have low pressure on the ground when the air pressure gets less as you go up in the atmosphere? The pressure should always be high. And where it is hottest like the Sahara desert where the high pressure is … you know the convection thingy (i.e. the atmospheric circulation model) … well this is where the air should be rising not sinking.”

Now, I could suggest numerous strategies for tackling such muddled thinking but I think a better starting point is to highlight some key common misconceptions in physical geography that seem to confound students. Armed with this knowledge as teachers we can be aware of potential pitfalls in the concepts and content presented in the classroom. And with these in mind, we can be more mindful over whether the ideas we are intending to convey are, indeed, being understood in a way that will ultimately make ‘accurate’ sense of the geographical world for the students.

So, for starters, here are four commonly held physical geography misconceptions

1. The mantle is semi-liquid or semi-solid.

The interior of the earth as a liquid has a long history as a ‘common-sense’ way of accounting for magma at the surface (volcanoes) due to rising from the Earth’s liquid mantle. More recently plate movements are commonly attributed to convection currents and students are familiar with liquid convection, not solid convection.  Analogies may use liquid convection examples (pan of soup and crusts etc.). Additionally, many educational videos refer to a molten internal layer. Diagrams and animations often show the mantle in orange/red colours that are associated with hot molten (liquid) (molten) materials. In reality, we know from seismic wave evidence that the mantle is almost entirely solid. However melting does occur, in areas where the upper mantle is decompressed e.g. at divergent margins, or where water is added to the mantle e.g. in the mantle wedge above a subducting slab. The processes generating melt in the mantle should be taught and discussed with students – and in my experience these idea can be introduced and understood successfully at Key Stage 3.

2.  Weathering and erosion

Students often confuse and/or conflate weathering and erosion, thinking the processes are the same. This is understandable as (i) both these processes change the appearance of the physical landscape, (ii) one (erosion) is often contingent on the other (weathering) and (iii) they often operate in tandem. And in the general public arena the two terms are commonly used interchangeably, which can confuse students. Weathering is often understood as caused by weather, but it is climatic conditions acting over longer timescales that control the type and rate of weathering (it seems a pity the process was not originally termed ‘climating’!).  A common issue is that both these topics are taught with emphasis on learning specific processes, e.g. freeze-thaw, abrasion and so on, with insufficient link to check students’ understanding whether the process leads to breakdown/decay (weathering) or removal (erosion) of material.   Another idea to clarify is the classification of weathering types i.e. mechanical is due to application of a physical force, and chemical is due to a reaction, usually involving water or moisture. Biological weathering is an unfortunate ‘addition’, because it can be either physical or chemical or both! In fact, the biology (e.g. tree root) is the agent that causes the weathering, much as ice is the agent of freeze-thaw wedging. Getting students to identify the agents responsible for particular weathering (and erosion) processes is helpful. And an important ‘myth’ to dispel is the single agent/process in weathering or erosion, e.g. all chemical weathering is caused by acid rain, or cracking and flaking of rocks is caused only by freeze-thaw process. Other agents and processes are available – as careful observation will often reveal!

3. Glaciers operate like bulldozers.

Students are taught that a valley changes from a V-shaped profile and enlarged into a U-shaped valley due to glaciation. Often, they are also told that a terminal moraine is sediment dumped by the glacier as it melts.  Having been told that a glacier moves (flows) downhill, students often make sense of the valley excavation and the ‘classic’ arc shape of a terminal moraine by thinking the process is like a bulldozer i.e. material is pushed out of the way by the power of the glacier and is piled up at the front (snout). The idea of the glacier retreating often compounds the misconception as the students liken this to the bulldozer reversing, and leaving the debris piled up in a moraine.

If an analogy is to be used, then the glacier acting as a ‘conveyor belt’ is probably better, but this can also be problematic as it implies sediment is only carried on the surface of the glacier. It is generally better to explore how glaciers move, erode and deposit within and at their margins.

4. The Greenhouse effect and the C0₂ ‘bouncing barrier’ layer.

Most students will explain the greenhouse effect being as the sun’s heat energy bouncing off the Earth and hitting a ‘barrier layer’ of C0₂ in the upper atmosphere, so the heat bounces back and is trapped warming the atmosphere.  This simple, but wrong, idea undoubtedly dominates students’ minds because unfortunately the greenhouse effect is shown as a ‘barrier- bouncing’ process in many textbooks, web-pages video clips and animations, which reinforce the idea that there is a layer of greenhouse gases in the sky acting like a pane of glass in a greenhouse, trapping the heat that originally came as visible light from the Sun.

The ‘barrier layer’ of C0₂ doesn’t exist!  C0₂ is diffused and mixes evenly throughout the atmosphere (with very small variations at sources and sinks). And, at an altitude of about 5-6 km the concentration of greenhouse gases in the overlying atmosphere is so small that heat can escape freely to space. Also, ‘bouncing back’ gives the impression of reflection as the dominant process – but this is not how the greenhouse effect works.

Earth’s energy budget showing inputs and outputs at the Earth’s surface. For full explanation see
https://earthobservatory.nasa.gov/features/EnergyBalance
(NASA illustration by Robert Simmon. Photograph ©2006 Cyron.)

Of 100% incoming solar (sun) radiation energy, about 23% is absorbed directly by the atmosphere, 29% is reflected back into space by bright surfaces (like clouds and ice), 47% is absorbed by the Earth, of which 17% is returned by terrestrial radiation (heat) energy.

Students need to be focussed on energy transfer (and heating) by radiation. This can be difficult to comprehend because it is not easy to see, but a helpful illustration/ demonstration is to use student experiences of brick or concrete (paving) surfaces left in sunlight, which later feel warm for some time (out of the sun). This is terrestrial (or longwave) radiation – converted from solar (shortwave) radiation – it is useful to distinguish between these with students.  

In atmospheric gases made of three or more atoms, i.e. CO₂ (but also H₂O, CH₄ and N₂O) the atoms are held together loosely enough to absorb terrestrial radiation easily and the extra energy causes them to vibrate, producing heat. Gases with two atoms like Oxygen and Nitrogen can’t do this easily. Eventually, the vibrating molecules release the radiation in all directions, which will likely be absorbed by another greenhouse gas molecule (some may escape into space). This energy then re-radiates back toward Earth and heats both the lower atmosphere and the surface, adding to that received from direct solar radiation. Increased levels of CO₂ in the atmosphere means an increase this process and increased atmospheric (global) warming, but this is not due to any ‘bouncing barrier’ acting like a pane of glass in the sky.

An excellent resource for classroom discussion to consolidate (accurate) understanding about the greenhouse effect can be found at  https://www.earthlearningidea.com/PDF/310_Greenhouse_effect.pdf

Over to you…..

What other physical geography misconceptions have you encountered with your students – or perhaps you think you might have misconceptions or slightly muddled knowledge about an important idea in physical geography?

Please do tell us about your experiences by leaving comments in the reply box below – it’s useful to share, and we will do out best to clarify any misconceived physical geography.