January 17, 2013
LASI V: Field Trip Introduction
Posted by Evelyn Mervine
Back in late October and early November 2012, I attended the LASI V Workshop on the “physical volcanology of subvolcanic systems: laccoliths, sills, and dykes” as an observer and science writer. The workshop started out with 2 days of talks at the Pine Lodge Conference Centre in Port Elizabeth, South Africa. Recently, I have been writing about some of the research that was presented during these talks. I’ve already written about Dr. Volcano in the Cave of Crystals, Naica, Mexico and Xeno-Pumice: Mysterious Floating Rocks of the Canary Islands, and there’s more coming soon! However, I thought I should also start sharing some information about the wonderful LASI V field trip, especially since some of the research presented during the talks was about the remarkable subvolcanic systems that can be observed in South Africa’s Karoo Basin.
Today, I just want to give a quick introduction to the field trip route and the locations visited. In my next field trip post, I’ll give a general overview of Karoo Basin geology. Then, I’ll share some information and plenty of pictures from the various LASI V field trip stops. We visited so much great geology that I might not have time to cover everything, but I’ll do my best!
The LASI V field trip lasted 3 days. The map below shows the main locations visited during the field trip.
Here are the places that we visited during the field trip:
Day 1: We drove from Port Elizabeth to Aloe Grove, which is located just outside of Queenstown. On the way, we visited outcrops of Dwyka tillite and Ecca Group deep to shallow marine sediments. We also visited Elandsberg Mountain, where dolerite sills have been intruded into fluvial sandstones of the Beaufort Group. While we were at Elandsberg, we spent quite a bit of time looking at a dolerite sill with impressive spheroidal weathering. Finally, we visited Waterdown Dam, where there are some remarkable granophyre dykes that were produced by the interaction of dolerites and sedimentary rocks.
Day 2: We spent all day exploring the saucer-shaped sill complexes in the Golden Valley.
Day 3: We visited a place known as Witkop III, a hydrothermal vent complex.
That’s all for now. More about the field trip soon!
I was delayed by the theft of my laptop and other events, but I finally got around to posting some pictures from the LASI V field trip today :-).
I was interested to come across your photos of the WitKop diatreme. I was a faculty member at Rhodes in the 1970’s and a student and I looked at the diatreme. More recently I came across a paper in the Journal of the Geological Society of London with interpretations that differed from ours so I wrote a Discussion (Lock, Brian E. and Jock v.A. Robey, 2007, Discussion on Structure and Evolution of Hydrothermal Vent Complexes in the Karoo Basin, South Africa: Journal of the Geological Society, London, v. 164, p. 477-479.). We interpreted the structures you see as erosion and damp accretion bedding in a strong current of steam whistling up the phreatic vent. I would be interest in any of your observations in this regard.