Monday, January 24, 2011

Tswaing Crater

Tswaing Meteor Crater, Near Pretoria 2011

Tswaing Crater Climate Record
Tswaing means place of salt in seTswana - a language I spoke fluently as a child but have now unfortunately mostly forgotten. It is also the name for a remarkable feature in the landscape outside Pretoria, South Africa, that was formed 250 million years ago when a meteorite slammed into the Earth at a velocity of nearly 20km/second. Walking around the crater last week during the "record setting" 2011 La Nina flooding in the region, with the lake level the highest a local geologist had ever seen, I was reminded of how long term paleo-variations in regional hydrological balance are usually far greater than anything in the modern record. Tim Patridge cored the Tswaing crater some years ago. Granite at the bottom of the core proved the crater was not a volcanic feature, while the sediment layers recorded the attached incredible record of monsoon variations, with extended periods both far wetter and far dryer than today. Interestingly the ~100 thousand year 'glacial-interglacial' signal associated with changes in eccentricity in the Earth's orbit that is so familiar in most long climate records is completely absent. Instead there seems to be a strong ~40k oscillation perhaps linked with changes in obliquity (tilt of the earth's axis). Though infinitesimal on these vast paleotimescales, I managed to click my own record of temporal change. Below a snapshot of me (taken with a twin lens reflex rolleiflex camera!) standing on the wall outside the Union Building in Pretoria in 1966, and the same wall recaptured (with my iphone) in digital color in 2011.

Wall outside Union Building, Pretoria 2011

Me and NaiNai at the same wall in 1966