Scientists planning to drill deep into the Alpine Fault to understand more about faults and earthquakes can thank Harold Wellman for discovering the fault nearly 70 years ago
Last week, Victoria University of Wellington reported that a team of 60 international scientists are gathering at Franz Josef on the West Coast to develop a drilling plan for a major investigation of the Alpine Fault. Led by John Townend of the School of Geography, Environment and Earth Sciences, the team aims to establish a deep “fault-hosted observatory” similar to one already established on California’s San Andreas Fault.
Satellite photographs show the Alpine Fault, which at 650 km in length is one of the world’s longest active fault lines, as a dramatic line at the western base of the Southern Alps. Its position bisecting the South Island from Blenheim to Milford Sound marks the intersection of the Pacific and Australian tectonic plates, and separates the different rock types of the western and eastern South Island. Victoria News reports that as well as penetrating the earthquake zone and removing rocks for analysis, Townend’s team “hope to install a variety of underground instruments that may shed light on the timing and severity of earthquakes and other forms of tectonic deformation on the Alpine Fault”. There’s also a chance they might catch an earthquake in action – the Alpine Fault is understood to produce earthquakes of magnitude 7.9 every 200 to 400 years, and since the last rupture was in 1717 the fault is understood to be late in its earthquake cycle.
Seventy years ago, before the advantages of satellite photography and the development of the theory of plate tectonics, the Alpine Fault had not even been discovered, let alone investigated. One of my favourite paintings, Hairy Mary Creek by Bob Kerr, shows Harold Wellman and Dick Willet at Hairy Mary Creek, just north of Franz Josef, where the schist rock is shattered like crumbled weet-bix and the Alpine Fault is exposed to view. It was on a 1941 field trip that these New Zealand Geological Survey geologists realised there was an enormous fault running almost the entire length of the South Island.
They were distracted from a South Westland search for mica that was needed for wartime radio condensers by the Gregory Valley fault, which they believed they could trace further than was shown on their crude geological map. Trudging through heavy rain, washed out tracks and swollen rivers, they followed the fault south along the base of the mountains, realising it was part of a much bigger unmapped fault. They published their findings in 1942, along with a map showing the position of the Alpine Fault.
Seven years later Wellman made an even more startling discovery. Wellman proposed the radical idea that the Alpine Fault had moved 480 km, laterally. As Simon Nathan wrote in his biography of Harold Wellman, A Man Who Moved New Zealand, “The idea had come to him on a wet Sunday afternoon when he was sitting at the dining room table in Greymouth, and he immediately took a pair of scissors and cut a copy of the newly published geological map of the South Island along the Alpine Fault to see if the opposite sides matched. There was excellent agreement, and this seemed to explain all sorts of problems in the distribution of rocks in the South Island.” Wellman’s controversial idea was ridiculed at first – at that time faults were understood to move vertically but not laterally – but his idea gradually gained acceptance over the following decades.
I had the privilege of meeting Harold Wellman several times in the 1980s. As I recalled in my 2005 Listener review of Simon Nathan’s Wellman biography, on Friday afternoons Wellman would often turn up at the geology seminar room at Victoria University, with woolly jumper and battered briefcase, brows furrowed ready for a fight. Over a few drinks in the nearby staff club, the retired professor would argue about geology with the younger academics – and the students if they were game – until it was time to catch the bus home. As a student there at the time, I didn’t yet know that this likeable curmudgeon was one of New Zealand’s most distinguished geologists.
Wellman’s discovery that the Alpine Fault had moved 480 km is still one of the most astonishing and, ahem, groundbreaking scientific discoveries in New Zealand’s history. Good luck then to John Townend’s team, in hope of some remarkable discoveries of their own.