The real story behind our mountains
Mountains are formed when landmasses are squeezed and folded upwards, but, until the 1940s it was incorrectly thought that this was because the Earth was gradually cooling and contracting.
It was a New Zealander, Harold Wellman who disproved this idea with a spectacular discovery. This discovery also significantly contributed to the most important theory underpinning much of modern geology.
Born in England in 1909, Wellman moved to New Zealand when he was 18. He started work as a clerk with the Union Steam Ship Company of New Zealand but later qualified as a surveyor, however in 1931 the Depression left him unemployed. Being something of a maverick, he took off to the West Coast to prospect for gold. Fortunately, the Department of Scientific and Industrial Research (DSIR) were carrying out geological surveys for mineral resources and Wellman joined a team looking for copper. He found he had a talent for geology but was told that to advance he really needed a degree in the subject. This motivated him to start studying part-time for a BSc which he completed in 1939.
In 1940, on a trip to south Westland to look for mica, a mineral in high demand because of its use in radio components, he noticed two distinct types of rock on the river beds; schist and granite washed down from the mountains. Granite contains the minerals quartz and feldspar subjected to huge pressures. It is an igneous rock, that is one formed from the cooling and solidification of lava.
Schist is a metamorphic rock, one changed profoundly both physically and chemically when subjected to high temperature and pressure. These rock types formed separately under very different conditions and Wellman reasoned that somewhere there must be a boundary between the two source rock formations.
Earlier work further north in the South Island had revealed that low, wooded, conical hills were mainly granite. From his truck as he drove on his way down the west of the South Island, Wellman could map the bedrock just by noting the locations of these hills and in so doing, established that the boundary between the granite and schist lay at the foot of the Southern Alps.
The boundary turned out to be the longest natural straight line on the Earth – 600kms, covered in thick bush it had previously been unnoticed. Wellman’s line was a fault whose presence was only revealed where rivers crossed it.
The rock on the boundary between the granite and schist had been crushed as the two faces of the fault scraped passed each other; the heat and pressure had chemically altered the rock to produce a distinctive green powdered clay mineral called cataclasite.
Wellman’s studies further revealed that the combination of rock features 500kms to the north on d’Urville Island and in the Nelson area were exactly the same as those found in Southland-Otago. Two huge plates of the Earth were slipping passed each other and had shifted parts of Southland all the way north to d’Urville Island.
In the 1940s this was a revelation and when Wellman reported his finding at the 1949 Pacific Science Congress in Christchurch it was viewed with scepticism. Faults on this scale severely challenged existing geological theories.
Wellman was not disheartened, he went on to identify a series of faults which not only moved the ground horizontally but vertically and he also linked the movement of faults to recorded earthquakes. The idea that continental plates moved slowly across the planet, bumped into each other and crumpled landmasses to form mountain ranges such as the Southern Alps was formulated in the early 1960s. Many scientists contributed to this theory of ‘‘plate tectonics’’, which was a sensation at the time and entirely consistent with Wellman’s findings.
Perhaps a measure of the international importance of Wellman’s work was the 1992 documentary by the prestigious BBC Horizon team, ‘‘The Man Who Moved the Mountains’’.
It acknowledges Wellman’s discoveries and the important role he played in the theory of plate tectonics. In 1970 Harold Wellman became professor of geology at Victoria University in Wellington and, largely unknown to the New Zealand public, died in 1999 having taken his place as one of the great geologists of the 20 th century.