From Earth Science On-Site
Snableazes & Cullernose Point, North'berland
It is anticipated that the ideas and materials presented here will be adapted by schools, and others, to be more appropriate for their own purposes and programmes of study.
In such circumstances please acknowledge the source as the Earth Science On-Site project.
Many ideas involved in this Earth-Science On-Site excursion will revise ideas from Key Stage 3 work. See document SNA6 KS3 prep.
At Key Stage 4, in addition to the knowledge and understanding of geological processes gained in Key Stage 3 Physics, the pupils’ knowledge of the response of materials to deforming forces, needs to be revised and slightly extended. See parts 1 and 2 below.
In addition to the Key stage 3 concepts the following themes should form the basis of the preparatory lesson in school within a week prior to the field visit. The three themes are focused on understanding faulting, folding and igneous intrusion.
Part 1: The Response Of Materials To Bending Forces
Time: about 15 minutes
In KS3, pupils are likely to have investigated the behaviour of springs and rubber bands when they are stretched. Under lower stresses, both show a linear relationship (known as Hooke’s law) between force (load) and extension. This is called elastic deformation. However as the stress increases, the behaviour of the two materials begins to differ; neither obeys Hooke‘s law any more, but the spring becomes permanently deformed, while the elastic band becomes much more difficult to stretch further, and eventually snaps, demonstrating brittle failure.
However, it is unlikely that pupils will have investigated behaviour of materials under bending forces. For the purpose of this preparatory lesson, a few quick qualitative demonstrations should be enough to achieve the following learning objectives:
For quick demonstrations the teacher will need to ‘sacrifice’ e.g. a few (old) wooden rulers (or wooden skewers), a few (old) plastic rulers (or similar plastic strips which do eventually show brittle fracture) and a few metal (steel) rulers (or similar metal strips which can be bent by hand). If a variety of metals in strip form such as copper, zinc, aluminium, are available for comparative purposes, so much the better. A steel wire coat hanger could be used to show brittle fracture after ‘working’ in the plastic stage.
Part 2: That Folds Are Formed Gradually, Under Compressive Stresses
Time about 20 minutes
The beds on the Boulmer foreshore are simply tilted to the SE, but the beds at Cullernose Point have been folded. The north –south trends of the folds indicate an east-west compressive force, perhaps created in association with the stresses which also caused nearby faulting.
The activity below is taken from the Earth Science Education Unit (ESEU) workshop “The Dynamic Rock Cycle”. Visit the Earth Science Education Unit website for free materials relating to the teaching ideas of The Dynamic Rock Cycle. Contact firstname.lastname@example.org for details of their facilitator scheme for free In-Service Training for science departments, funded by UK Gas and Oil.
Part 3. Make Your own Folds
Equipment: a box with transparent sides (a chocolate box, or component drawer.) a spatula or desert spoon, a tray (to catch spilt sand) a cardboard paddle to fit snugly across the box, 500g of dry fine sand, 25g of flour, a photograph of folded rocks, digital camera (optional).
Teachers may want to do this as a demonstration, or, with multiple kits available teachers may want pupils to complete the exercise in small groups and discuss it afterwards to draw out the learning points.
Procedure: Place the cardboard paddle vertically at one end of the transparent box. Then build up several layers of sand and flour, but DO NOT fill the box more than half full. (It is useful to place the flour layer ONLY against the front face of the box, thus using less flour, and making the sand re-useable a second and third time.) (See Figure 1)
Very carefully, push the vertical paddle across the box, so that it begins to compress the layers. When you notice the layers beginning to bend, stop pushing. Hold the paddle upright and take a digital photograph, or draw a scaled diagram of the result.
Continue pushing the layers with the paddle until the sand is about to overflow the box. Hold the board upright and again photograph or draw a scaled diagram of the result. It should have features looking something like Figure 2. Photographs or sketches of the intermediate stages are also instructive.
The Discussion: Describe the folded nature of the layers, bringing out the following points;
Part 4. Igneous Processes
The central feature of this Earth Science On-Site visit is observation of igneous (dolerite) intrusions. The large dyke at Boulmer, (cutting across the bedding) and the sills at Snableazes and Cullernose Point (roughly parallel with the bedding) require some preliminary understanding of the geometry and origins of such features and their relationship to the bedding of the country rock they intrude.
Activity 1: Although videos and three-dimensional models are useful for establishing the main ideas and definitions, the ESEU workshop demonstration “A volcano in the laboratory” and the “Lava in the laboratory” pupil activity are extremely useful for demonstrating the processes involved, using red wax as a proxy for intrusive magma, and syrup as a proxy for extrusive lava.
Activity 2: Pupils should examine and describe crystalline igneous rocks and relate the crystal size to rate of cooling, and the overall colour to acid or basic magmas. . E.g. Granite, and rhyolite (both acid rocks), and basalt and dolerite (both basic rocks).
A summary of the central ideas and definitions is given below.