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school children. Here, along the base of the cliff sat a line ofabandoned houses where roofs were punched with holes andencircled by newly fallen rubble. Atop the cliff, another cluster ofabandoned houses stood at strange angles, rooflines askew.Evidently, the location of houses below these cliffs (comprised ofa series of ash layers, basalt and ignimbrites) was not consideredto be a problem at the time of construction. This scene of rockfall-relateddamage continued throughout the suburb of Sumner,which was badly affected by the 21 February 2011 earthquake.Another major cause of building damage was liquefactionand lateral spreading in riverbank gravels along the HeathcoteEstuary and Avon River. In Avonside, street after street of houseshad been abandoned as ground ruptures affected the buildings’foundations and/or structural integrity. The uneven road was thefirst indication of subsidence, although it was not until we tooka closer look at street level that we saw why these houses wereempty. In one instance, a surface rupture ran across the frontyard of one house, affecting the foundations, and then continuedthrough the side fence to damage the neighbouring house. It wastragic to see these charming houses with their leadlight windows(built from the 1880s to 1920s) in such a depressing state. Itseemed the old weatherboard houses survived the lateral spreadingbetter than the brick houses. Bricks made of Sumner rockhave a flat top and base and therefore provided no flexibilityduring the earthquake.Next we were shown a study site adjacent to the Avon Riverwhere Masters student Sarah Baston is looking into theliquefaction history. Her trench revealed multiple generations ofliquefaction and paleoliquefaction, indicating that there waspre-Darfield seismicity in the area. In total, 150 houses were lostto cliff collapse and rockfalls, while roughly 6000 houses werelost from liquefaction and lateral spreading.We then wound our way through the back streets towardsthe CBD. At one stage a road closure and road repairs made usturn around. Finally in the CBD, we noted many of the historicbuilding frontages were boarded up and fenced off at the awningfor pedestrian safety. Orange bollards and signs declared ‘RoadClosed’ or ‘No Public Access’. There were excavators clearing awayrubble in empty building sites, and then there were whole blocksof damaged buildings, some with scaffolding, others covered withtarpaulins. One building had been recently demolished, leavinga pile of jagged rubble and dust. We were able to take a shortwalk down to the Christchurch Cathedral site cordoned off byhigh fences. Scaffolding was present where the steeple oncestood and another wall had started to crumble away. It wasobviously once a magnificent building and as it was located atthe heart of the city, it represented much more than just acathedral. Places where building damage is most severe aroundChristchurch have been mapped as ‘Red Zones’. These zonesclosely correlate with gravel point bars along the Avon River,which are sources of liquefaction throughout Christchurch.Group photo in front of Lake Poerua, Inchbonnie, near to surface expression of the Alpine Fault. Photo courtesy Emma Mathews.TAG December 2012| 39
The Greendale Fault where it emerges at Highfield Road. Displacement ofthe fence line and hedge show the amount of extension and uplift thatoccurred along this part of the fault. Image courtesy Emma Mathews.After a welcome lunch, we continued to travel west acrossthe green pastures of the Canterbury Plains towards Darfield.Grey skies persisted. At the eastern end of the Greendale Fault(GF), it emerged as a kink in the railway line, and had beensmoothed out since the earthquake. The countryside was slightlyundulating, but we could see the evidence of uplift and extensionin a small rise of the tracks and abrupt change in the height of anearby hedge. Now we had our eye in for these subtle landscapechanges as we moved to the next stop on Highfield Road. Thiswas the site of major surface rupture of the GF as it crossed theroad. Although the road had since been resurfaced, the largehedges and fences lining the road still show the GF trace. Bothhad marked offsets and were no longer in a straight line. The sitewas also on a rise, higher than the surrounding landscape, whichwe were told was flat before the Darfield earthquake! Interestingly,the magnitude 7.1 quake occurred on the Charing CrossFault to the north of the GF, which triggered GF movement.Following our visit to the GF, we travelled into the alpineareas of Porters Pass and Arthurs Pass towards Inchbonnie. Therewas so much more of the tectonic regime and structures to seein the remainder of the trip. But the ongoing effects of theDarfield and Christchurch earthquakes on the daily lives of thepeople of the city are what will linger in my memory. The mediacoverage has stopped in Australia, but the damage aroundChristchurch is significant. This part of the trip was memorablenot only for the effects of the earthquake, but also becauseI don’t think we left the coach without our raincoats for theentire day!EMMA MATHEWSACT Division34th IGC — Symposium 1.1on Geoheritage, Geoparksand GeotourismConveners — Bernie Joyce & José BrilhaA strong ProGEO presence from Europe and many presentationsfrom other countries across the globe, with sessions running overthree full days, made this symposium the biggest internationalgathering to meet in Australia to discuss the three G’s —Geoheritage, Geoparks and Geotourism.A total of 44 oral presentations included keynotes by KevinPage, Patrick McKeever, Ross Dowling and Jonathan Tourtellot.Fifteen posters were displayed for discussion. Total attendance,with numbers up to 80 at a time, can only be described asexcellent. Also making major contributions to the smooth runningof the symposium were Margaret Brocx, Lars Erikstad, ChangxingLong and Angus M Robinson.The final day concluded with a session entitled ‘Finaldiscussion and plans for the future’ led by José Brilha. Theconclusions reached, and other details of the meeting, togetherwith the final version of the Geoheritage Symposium program,will remain available on line at http://web.earthsci.unimelb.edu.au/Joyce/heritage/IGCGeoheritageSymposia2012.html.Additional news will be added to the website from time-to-time.A full symposium report is being prepared by Ian Lewis andwill be published in the journal Geoheritage soon.Manuscripts are being solicited for a special volumeof Geoheritage and should be uploaded now to http://www.springer.com/earth+sciences+and+geography/geology/journal/12371.BERNIE JOYCEOne of several post-conference excursions in the Brisbane area included theTweed volcano, with Warwick Willmott, doyen of Queensland geologicalheritage studies, as one of the leaders. Image courtesy Sung Rock Lee.40 |TAG December 2012
Page 2 and 3: The Australian GeologistNewsletter
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