This is a collection of unusual structures on the underside of a small sandstone overhang. It’s made of different material than the surrounding sandstone, it’s a hard to the touch with no visible sand grains. Most of the surface is made of tiny nodules that almost look like condensation on a cold surface. In the center is a more prominent raised area that looks like a cast of an animal burrow.

More data from the BOM, this time I’m plotting their historical tidal measurements along with moving averages over 6 months, 1 year, 5 years, 10 years and 30 years. Tidal measurements are for Sydney taken from the Fort Denison gauge, the data includes monthly averages for low and high tides and the mean, going back to 1914. Like the temperature data there are local rises and falls that last 10 years or more, but the consistent long term trend is up. Click through to have a play with the chart, select the data sets you want and they will be displayed.

Besides the boring old weather the Bureau of Meteorology website has a lot of pretty cool stuff. Something I’ve been digging into lately is their climate data. Depending on the weather station you can find rainfall, maximum and minimum temperatures going back over 150 years. I’ve used their temperature data for the Observatory Hill station in Sydney to make a graph over time, I’ve also calculated moving averages over various time periods. It’s turned out some pretty interesting results. There’s a clear warming trend since the early 1900’s for maximum temps and around the mid 1940’s for minimums, but it’s not all smooth, there have been some ups and downs that have lasted over 10 years. Click through to the interactive graph and have a play, you can turn the various data series on and off to compare. You have to be a bit patient, it can take a few seconds after you click to send through the new data points and graph them.

Ever wondered about the soil in your area? Where did it come from, what will grow in it, how does it respond to flooding or drought? Apart from being of gereneral interest these questions are pretty important depending on what you want to use the land for.

Any construction requires knowledge of the soil’s physical and chemical properties such its stability, will it deform when wet, how far down to bedrock, is the soil corrosive? And if you want to grow anything: Is the soil fertile, is it acidic or basic, clayey, sandy, are there any salinity problems?

One of the reasons Mt Tomar supports such lush vegetation is that it’s soil derives from the basalt which caps the mountain. Basalt is a very fine grained, dark coloured rock of volcanic origin. It’s abundant in iron, magnesium, calcium and other elements and weathers to form a mineral rich soil that plants love.

I was hoping to see some of the basalt flows but the weather was pretty miserable so we didn’t spend as much time as I would have liked looking about. I did notice the garden walls just below the visitors center were made from presumably local basalt columns. A closer look at the rocks revealed olivene phenocrysts and small vesicles some of which were lined with white crystals, possibly calcite or aragonite?