Search This Blog

Friday, 18 November 2016

A visit to the Sydney volcano

Looking east, near Green 4.
Yes, that's right, Sydney has a volcano — or at least a remnant in the form of some contact metamorphism.  The last time I visited this was 41 years ago, and I had trouble finding precise information on the web, so this post is in part to save others the searching annoyance I had. The assorted technical words are there to catch the attention of people's web searches. The rest of you, just enjoy the views, OK?

The short version: look for the structure on the right, and go around to the left of it. The neck will be in front of you. The coordinates are, near enough, -33.887471, 151. 285581.

Detailed version
Looking south, on the coast, southern end of golf course
On the premises of the North Bondi Golf Club, there is an outcrop of sandstone which has been turned to quartzite. The standard view is that this is the result of contact metamorphism from a volcanic neck that burnt its way through the Triassic Hawkesbury sandstone. There are also a number of weathered dykes in the area.

The location is near Green 4.  I got off the 380 bus near Wallis Parade, scrambled up the slope to the golf course, and made my way cautiously across course.  After a bit of poking around to the south, where I saw this amazing pair of weathered-out dykes — or is it a trio?
I think the left-most is just a joint.

No matter, I found the columnar jointed quartzite when I clambered on top of the sandstone structure in the first picture, found a tee, and then looked down.  I scrambled back down the quite daunting sandstone stairs (no hand-rail!), and went around to get my shots. 

Looking north from the quartzite
I then took one more shot to guide those coming behind me. The chimney from the sewage treatment works (top left cornert) is a good landmark, and I was looking north here, from just beside the quartzite. You can just see North Head in the distance, out on the right.

That left that part of my morning done, so I skittled back down to the road to catch a 380 bus further north, getting off at Macquarie Light, a remarkably early Sydney structure.

MACQUARIE TOWER and LIGHT, is situated on the highest Part of the Outer South Head of Port Jackson Harbour, in Latitude 33° 51’ 40” S and Longitude 151° 16’ 50” E. from Greenwich. The Height of the Light from the Base is 76 Feet; and from thence to the Level of the Sea 277 Feet, being a total Height of 353 Feet.—The Inner South Head bears from the Light-House N. by W. ¾ W. distant 1¼ Miles. The Outer North Head bears from it N. by E. 2 Miles. The Inner South Head and Outer North Head, lay N. E. ½ E. and S. W. ½ W. of each other, distant 1 1-10th Mile. The Light can be seen from S. by E. to N. by E. Those lines of Bearing clearing the Coast line ½ a point each way, and may be discovered from a Ship’s deck on a clear Night, 8 Leagues. The North End of the Sow-and-Pigs Reef bears from the Inner South Head, S. W. by. W. ½ a Mile. N. B. The Bearings are Magnetic, and the Distances computed in Nautic Miles. The Variation 9° Easterly.
(signed) J. Oxley, Surveyor General.
Sydney, New South Wales,
29th April, 1818.
The Sydney Gazette and New South Wales Advertiser, 20 June 1818, 1, http://trove.nla.gov.au/ndp/del/article/2178010

Cactus (probably Opuntia, a weed.)
 After that, it was plants. I have been teaching my young charges at Manly Vale Public School this week, and one of the things I introduced them to, in my role as "visiting scientist", was the one on the left, Kunzea ambigua, which is important on North Head, and hard to photograph. I was fairly satisfied with this one, though I was happier with the bee that was burying itself in a cactus flower.

Still, this last one would have pleased my children most, because I introduced them to the art of determining gender in she-oaks, an Australian and Pacific native genus.

They delighted in spotting the trees and shouting "boy-tree" and "girl-tree", once they cottoned onto how to tell which was which. This Allocasuarina distyla is a girl-tree, as they would all have known, because they now recognise male and female flowers.

I have no idea what the long-term effect will be of my teaching them that particular skill, but I am sure that in some way, it will have opened somebody's heart and mind to a new way of thinking.

That means I win!

2 comments:

  1. Replies
    1. Beadle, Evans and Carolin say A. distyla is "usually dioecious", so no.

      Delete