I’ve always been grateful to live on the edge of Berowra Valley National Park but a wonderful community event put on by Hornsby Shire Council at a park down our street opened my eyes to just how special my neighbourhood is. I thought I might share some information about the ‘Protecting our Forests’ campaign and Council’s efforts to raise awareness in the community.
While on a guided walk with a geologist through the Blue Gum High Forest I learnt that we live on the edge of a very unusual volcanic explosion called the Hornsby diatreme. It is a volcanic explosion that happened during the Jurassic age. For diatremes to occur, magma must enter horizontal sedimentary layers and encounter water! The groundwater then converts to steam (and to put it simply) blasts to the surface through powerful steam driven vents. Over time, as the vent weathers, rocks are blasted to the surface. It would have been quite astounding to both see and hear! While these are worldwide phenomenon, you would be hard pressed to find one that is better or a more accessible on this planet than the one on our doorstep!
There are 95 diatremes in the Sydney basin but the diatreme complex of Hornsby and Thornleigh is one of the two largest. If you live in the area, you will be interested to learn that this is what provided the metal aggregate in the quarry in our neighbourhood!  Diatremes are extremely fertile and the remnant Blue Gum High Forest here doesn’t grow anywhere else in the world except for Sydney’s north shore and it’s northern and north-western suburbs. It is an ecological community which means it is a unique and diverse combination of flora and fauna co-exisiting.
Sadly during the last ~200 years or so the forest has been cleared for timber, farming and urban development and today, less than 5% of the area the forest originally covered remains. It is now at at risk of extinction and has been listed by the NSW and Australian governments as a critically endangered ecological community.
There’s only 200 hectares of Blue Gum High Forest left on our planet. 14 hectares of this is what I wake up to every morning and 74 hectares remain in Hornsby Shire! That is as much an incredible privilege as it is a responsibility. We will all have to do our bit to make sure we help keep it alive so all the creatures that call this place home from the tiny micro bats and the glossy black cockatoos to the rare powerful owl and the ring tail possum, might also survive. The forest is also key to keeping our soils healthy, absorbing carbon dioxide, and protecting the incredible creeks and wetlands in the area. The Council flyer explains that they are both a window to our past and vital for our future.
As we walk through the forest our geologist guide explains that they have found some interesting fossils in the area both quite contemporary as well as ancient. Some of the fossils have been linked to those found in the Illawarra area so you can imagine the size of this blast. The blast created a crater about 400m higher than the level we live at now. Dinosaurs once roamed up here but the ground has eroded away. While looking through the plans, we realised that we live right on the edge of the diatreme, on the sandstone plateau.
If you live in a different part of Sydney, and you visit the north shore we would be happy to guide you on a bush walk. If you live in the area, make sure you plant some native species to encourage birds, mammals and butterflies, go on bush walks, remove weeds from your garden (note to self), volunteer in a local bush care group, and never let your pets wander in the bush.
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