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Heels 1976

A Study of Leatherwood-Tramper Interaction

page 36

A Study of Leatherwood-Tramper Interaction


The mechanism of mass loss during leatherwood-tramper interaction is dependent on the physical properties of the leatherwood bush. An equation describing the electrostatic charge buildup during the process is derived. Some tramper behaviour is analysed in the light of this phenomenum.


The problems relating to the restriction of human passage through alpine scrub (Harper, I896) and leatherwood (e.g. Law, 1975) in particular have been recognised through out the ages. Leatherwood often features in the Folklore and poems of the hills (e.g. Spearpoint, 1975). Pointedly, leatherwood is not mentioned in a thesis on the salube by MacPherson (1974).

Little quantitative assessment of Leatherwood-tramper interaction (LTI) has been reported in literature. In view of the large areas of leatherwood in the local ranges a research institute has been established for the investigation of LTI phenomena. This paper describes how static charge is built up on trampers during LTI and derives an equation relating the variables for this. It also discusses some of the consequences of this buildup of charge.

Field analysis

The individual leatherwood bush is a highly abrasive, firmly rooted object. Spikey twigs (Gooder,1971) and speartipped branches with high tensile strengths are surrounded by tough resistant leather leaves with sharply serrated edges (see illustration in Sissons, 1971 p.63). These components are several orders of magnitude harder and strongerthan the human flesh and its general cloth armour. Upon contact with the flesh and armour any one of these components causes molecular disarray and removes molecules, atoms and electrons from it (see also Radcliffe, 1974). Hence although a collection of leatherwood bushes (the leatherwood field) exhibits variations in surface tension and density, it always produces significant abrasion of a moving tramper. By application of the Schrodinger Equation,McLachlan (1963) showed why tramper page 37velocity through leatherwood is vanishingly small. However even entrained and effectively stationary trampers lose mass from the LTI due to the amplitude of their frenzied struggles. It is this loss of mass which leads to the buildup of static charge on the tramper.

Derivation of the Equation

Tramper is assumed to be a symmetrical object of total surface area S, totally immersed in leatherwood.

Area of one side is Equation .

Total volume of leatherwood displaced (sum of incremental volumes) is Equation where d is distance travelled in leatherwood field.

By Archimedes,apparent loss of mass M of tramper, Equation where D is mean field density.

However, because of the extremely abrasive nature of the medium, a proportion L of this M is actually lost.

Equation.where w and a are dependent on the state of the leatherwood and the armour of the tramper respectively.

L can be expressed as a sum,

L = L* + nm...2.where L* is mass of neutral particles lost; n is number of excess electrons lost; and m is mass of one electron.

Define a quantity F, the efficiency of excess electron production.


Substituting and rearranging in 1. and 2.,


Therefore total charge Q on tramper is

Equation DSd where c is charge on one electron.

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The quantities L, F, w and a are positive and real. They have been studied to a limited extent. For L≤Lc (critical total mass loss) for unarmoured trampers (Lc ÷ 20 grams), much of this loss is composed of neutral blood and body tissue. To the writer's knowledge, no reports of bone damage have been authenticated. Thus L is approximately equal to L* and Equation is approximately equal to F. However, trampers immersed in leatherwood fields have often been observed to have their hair standing on end. This is attributed to static electricity resulting from the removal of electrons from their bodies. Therefore F does not equal zero during LTI. For L > Lc hysteria usually occurs within a very few grams and results become inconclusive at this stage. This hysteria is presumably partly due to high charge density.

For naked trampers a is equal to unity. It decreases with increasing armour but reverts to unity when armour failure occurs after prolonged LTI. Both Lc and F increase with increasing armour.

The quantity w depends on the state of the leatherwood, but is relatively constant over a wide range of conditions. w seems to reach a maximum in old, leafless, thinly ice-glazed leatherwood fields.

L, F, w and a are effectively independent of the actual tramper. However, theoretically at least, F will increase slightly for weatherbeaten, thick-skinned trampers. Thus for different similarly-clad trampers in the same type of leatherwood field;

Q = constant. DSd.

Some Effects

Points of entry onto the tussock-covered ridges of the local ranges are rarely unguarded by leatherwood fields. Inevitably therefore, trampers on these ridges are slightly positively charged. This charge will be greater for larger trampers and for those travelling or attempting to travel long distances through large leatherwood fields. The effect will be most severe in such pedigree fields as on Tawirikohukohu.

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Aerial photography has shown that nowhere are these tussock ridges linear in any direction. Thus interaction of the charged trampers with the earth's magnetic field means circular and errant paths are probable. The writer and several of his Vuwtc colleagues have themselves described such circular paths unintentially on several occasions.

Large collections of trampers are seldom seen in one place on the tops because of the low probability of finding such charged entities in close proximity to each other. Related to this is the obvious danger of a party or pair trying to crowd into a hut, tent or sleeping bag after a long and severe period of Lti. Obviously the effect will be inoperative during low-level river travel. Consequently large gatherings are often seen in valley areas below the scrub line.


The equation Equation. DSd describes how charge is developed on a tramper during leatherwood-tramper interaction. It may help trampers avoid some unfortunate side-effects of traversing some hill country.

However, nothing is known of the maximum charges or charge rates or the decay of such charge accumulations. Nevertheless steps are being taken to install charge neutralisers at main road ends, and in strategic locations on the tops, of the Tararuas at least. These will be totally unobtrusive, and obviously more desirable than wholesale destruction of our native and intrinsically beautiful leatherwood areas.

J.R.Keys ( Technical Institute of Tramping Sciences.

Acknowledgements are due to members of Vuwtc for their sometimes willing, sometimes unwilling cooperation in the field; to Mr B.A.Sissons who refereed this work; and to Whatneys Hyperbolical Association for Research in the Realms of Yokels, for financial support.


Gooder, R.J., 1971. The Later Sixties. In Sissons, B.A.( Ed.) Vuwtc '71, Jubilee Magazine, pp 45 - 6.

Harper, A.P., 1896. Pioneer Work in the Alps of New Zealand. T.Fisher Unwin, London.

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Law, E., 1975. How to be a Missleader, Heels 1975, p.14. MacPherson, P., 1974. The Salube. Tararua 27, pp 39 - 40. McLachlan, L.A., 1963. A Mathematical Theory of Scattering off Leatherwood. Heels 1963, pp 10 - 11.

Radcliffe, P.K., 1974. There's a Creek I Know. Heels 1974, pp 12 - 15.

Sissons, B.A., 1971. (Editor ). Vuwtc '71, Jubilee Magazine. Spearpoint, G., 1975. Rain, at Arete Forks Hut. Heels 1975, p.23.