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Route Severity Diagram

By S.J. Collins

PART 3.  Constriction

Before we go on with the basic signs of the Route Severity Diagram, it is as well to remind ourselves that there are not really many things we have to learn.  There are only eight basic symbols, and we have already learned two of them, the signs for Passage and Pitch.   It is true that these eight symbols can be arranged to give a great deal of detailed information, but most of this information can be read from a Route severity diagram without bothering with too much detail. Just knowing the sign for Passage and Pitch will show you at a glance whether the cave is mainly vertical or horizontal for instance.

One of the main types of obstruction we encounter down Mendip caves is that of tightness, or Constriction.  The basic symbol for Constriction on the Route Severity Diagram is a sharp point partly blocking the passage like this……

…….and anywhere you see this sign, or anything like it on a Route severity Diagram, you will know that the cave is tight at that spot.

A tight passage will have a number of these signs along it, to remind you that it is still tight, like the ‘30’ signs which are repeated at intervals along a village street to remind you that you are still in a 30 limit.  The actual number of signs is not significant.  Neither is the way up they are drawn.  A Route Severity Diagram is not a plan nor an elevation of a cave, although it may be drawn to look more like one or the other.  Thus, all the signs we use have the same meaning whichever way they are drawn.    There is no ‘up’ or ‘down’ on an R.S.D. and directions have no meaning either.  The only thing that is ‘real’ about it is that if you come to a passage junction of two ordinary passages, the left turn and the right turn really do correspond with the turns you have to do in the actual cave.

Thus, all these signs mean ‘tight passage’……

What about tight pitches? Well, we have a sign for tightness and we have a sign for pitch.  Put them together and we will have a sign for a tight pitch.  The R.S.D. works like that, by building up simple designs to form a detailed picture of the cave in a convenient shorthand form.  Later on, we shall be able to describe things in much more detail.

Reads Cavern, Burrington

News has just reached the B.B. Office (!) that a collapse may have occurred in Reads Cavern.  Z Alley is reported to be blocked and two new chambers found.  The new chambers are reported to lie near the ‘Stone Age’ entrance.  The stream is also sinking near the cave entrance instead of well to the left of the cliff face.

Address Changes:

G. Selby, 913 West Olive Street, Corona, California, USA, 91720.
R.J. Price, G19 Test Equipment, English Electric Co., Kidsgrove, Staffs.
J.W. Manchip, 3 Blackthorn Court, Barnton, Edinburgh, Scotland.
E.G. Welch, 18 Station Road, Filton, Bristol.