Category Archives: Earth

Unusual Sandstone Formations

There’s no shortage of sandstone in the Sydney area, almost the entire extent of Garigal National Park sits on whats known as the Hawkesbury Sandstone. The Sydney 1:100 000 Geological Sheet classifies it as “Medium to course-grained quartz sandstone, very minor shale and laminite lenses” I wanted to highlight two sandstone formations, both of which are a bit of a mystery as to how they form.

I came across these formations on a trail run on a section of single track in Belrose that runs from the end of Ralston Ave down to the Bare Creek trail next to Bare Creek.

The first formation is called tessellated pavement.

tessellated pavement on the trail down from Ralston Ave to Bare Creek. Shoe for scale

There are a number of different types of tessellated pavement. The type I came across is seen on flat sections of sandstone that have been fractured into 4-6 sided geometric shapes. Some of the blocks are surrounded by deep grooves with rounded edges. It really looks like a man made road or path the way the blocks lock together. It’s not known how this structure forms.

The second formation is even more of a mystery.

Grooves and ridges on the trail. Is it rundkarren in sandstone?
The same formation with shoe for scale

It was on the same section of trail near the tessellated pavement. Found on a gently sloping section of sandstone, it had rows of deep grooves all running in the same direction from the top of the slope to the bottom. They looked like they could have been worn over many years by the trickle of water. Above the trail was a minor gully, there wasn’t any visible creek but it looked damp and swampy. In wetter times perhaps water could have drained slowly over the sandstone. This is all guessing, I couldn’t find any information on this type of formation. The closest I came was rillenkarren or rundkarren which is the weathering of similar channels in limestone by the slight acidity of the water dissolving the rock. Rillenkarren has sharper ridges and is thought to form out in the open while rundkarren is more rounded and thought to form under a superficial covering like sandy till, peat or a layer of plants and lichen.

Wikipedia

British geological survey

Speliogenisis

One Mans Funnies

Climate update

I’ve updated the climate pages with the latest data from the BOM.

If this summer felt long and hot to you then you’re right. The graph shows the average summer high is the hottest it’s been for 5 years. Looking at the 1 year averages the cooling trend that started in 2014 has reversed and we’re warming again. As always the longer term 30 year averages still show a very clear and consistent warming trend. The warming acceleration that started in 2013 is continuing.

Still no update from the BOM on sea level measurements, we’re stuck at the end of 2014 with that.

Rainfall data shows no clear long term trend, we’re pretty much smack in the middle of the historical long term measurements.

Sydney Climate Update

We’re just coming out of what felt like a freezing cold winter, it seemed like it was bitter and dark for so long. But when it comes to accuracy human skin and brain cells are really terrible at remembering and comparing the weather. Lucky for us we have the data!

Cold and wet at the Mt Tomah botanical gardens

The BOM have updated their long term climate data again. This time we’re in for a treat, we have updates to temperature, sea level and rainfall.

Looking at the maximum and minimum monthly temperature averages we have indeed had some cold months. The July average minimum of 8C is the coldest since 2002 when it was 7.9C, and looking back 30 years only 1995 was colder. The mean maximum for July was cool but many years have been cooler over the past 30 years. 2013 and 2014 were quite warm by comparison though, maybe that’s why it felt cold this year. As we’ve only got up to July we can’t compare moving averages yet.

For sea levels the short term averages actually show a drop in 2014. The 5yr and above moving averages still show an unmistakable upward trend.

Rainfall averages are up, I don’t recall it being particularly wet though, so much for memory.

Climate data update

I’ve updated the Sydney temperature and rainfall pages with the latest data from the BOM, we’re pretty much right up to date now, thanks BOM. Something has happened to their sea level pages though, their Fort Denison measurements have not been updated since the end of 2012.

It’s the long term trends that are of most interest so nothing mind blowing in these updates, temperature continues to rise on almost all average time periods. I found it interesting that even after the “August of rain” most rainfall averages are still low when you look back over time.

syd-temp