Post #2330543

2026-05-07 04:33 UTC

You can see how Sydney has sprawled out east across sandstone (pastel green) and shale (emerald green) to Camden and Penrith, and onto an alluvial floodplain (brown) to Richmond. Sandstone-derived soils are typically nutrient-poor, while soils derived from shale are generally more fertile. This difference comes down primarily to mineralogy: sandstone is composed mostly of quartz, a chemically inert mineral that releases virtually no nutrients as it weathers. Shale, by contrast, is rich in clay minerals and often contains organic matter, releasing a much broader range of plant-available nutrients as it breaks down. Additionally, the coarser, sandier texture of sandstone-derived soils creates larger pore spaces, which allows water to drain rapidly and leach whatever nutrients are present deeper into the profile and out of reach of plant roots. #geology #ecohydrology

Replies (3)

@natcbr@mountains.social 2026-05-07 04:42

I was surprised to learn after watching the new Netflix film Apex, that gniess (the rock the Troll Wall in Norway is comprised of) despite being a high-grade metamorphic rock formed from rock like granite at temperatures above 500°C makes for unstable climbing, compared to sandstone such as the Blue Mountains where parts of the film were shot is actually pretty good for climbing as I though it would be weak (although some can be weakened after rain). But when you think about the process it kinda makes sense; intense pressure forces minerals into parallel alignment i.e. foliation, which makes them weak along that plane, even if gneiss is very dense and has low porosity. #geology

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@natcbr@mountains.social 2026-05-07 06:39

Whilst alluvial floodplains are not ideal for permanent structures (for obvious reasons) they can make for amazing arable land. The Canterbury Plains in New Zealand are a prime example with its productive alluvial soils (though agriculture is highly dependant on irrigation) and is the dominant arable region in New Zealand, producing the majority of its grain and seed crops and supporting a significant dairy industry. The *most* fertile land in the country, however, is generally found in the Waikato and South Auckland. It's granular soils were built from strongly weathered volcanic tephra deposits, that largely originated from the Taupo Volcanic Zone. If you're wondering if there's a connection between NZ's tephra-derived soils and the dairy industry in NSW around Tilba Tilba and the aforementioned Gulaga: No, way too old. After 65 million years since the volcano where Gulaga now stands erupted, that process is essentially spent and whatever was there has long since leached away. Plus that volcano was a shoshonite-association complex including syenite and not the kind of basaltic or andesitic material that tends to weather into the most nutrient-rich soils. #geology #agriculture #NZ #NSW

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@oldclumsy_nowmad@mastodon.social 2026-05-07 04:59

@natcbr@mountains.social I enjoyed this series of posts on New South Wales geology for several reasons, including (1) I'm always curious about Australian geology, and knew next-to-nothing about NSW; and (2) I'm intrigued by gneiss and have been reading on that subject recently. Your comment on rock climbing in gneiss terranes is very interesting. Thanks for sharing that thought!

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