Mount Coolum

Mount Coolum has no business being where it is. You are on the flattest imaginable ground, a wide coastal sand plain running down to the beach, and then out of it, without warning or foothills or any gentle build-up, rises a great rounded dome of bare rock, right there beside the sea. It looks like something dropped from a height onto a billiard table.

In truth it was left, not dropped. Coolum is the hard trachyte core of a long-dead volcano, silica-rich lava so stiff it never really flowed but clogged the vent and cooled underground into rock far denser than anything around it. When the fires went out, tens of millions of years of rain and river set to work on the country, and everything softer was hauled off to the sea. The cone, the surrounding rock and the young coastal sand all wore away, while the plug, too tough to rot, simply stayed put. What you climb today is not the volcano but its frozen plumbing, a hard heart laid bare long after the mountain that made it had gone. Geologists have a tidy word for a hard lump left standing proud of a worn-down plain, a monadnock, and Coolum is one of the neatest on the coast.

Start up the track, though, and you begin in forest. The lower slopes hold enough soil, washed down and gathered at the foot of the dome, to grow open eucalypt woodland, with paperbarks, the melaleucas, crowding the damp swales where water lies. But climb, and the soil thins under your boots. Trachyte weathers with maddening slowness, and the higher pavements lie so bare and steep that hardly any dirt can gather; only gritty, skeletal soil, jammed into the joints and shallow hollows. The trees give out, and the top is held by a low, tight heath, hard-leaved and stunted, wedged into the cracks and bent flat by the wind off the sea. The leaves up here are stiff and small and armoured, the sclerophyll leaf worn for the plainest reason of all. There is next to nothing to grow in.

Walk out past the forested foot onto the open flat, though, and the country drops low and heathy again — but for the opposite reason. The sand plain wrapping around Coolum’s foot is wallum and coastal heath, and its soil is not missing at all. It is deep, and it has been leached over hundreds of thousands of years until barely a trace of anything useful survives. So the dome and its apron both wear the same low, hard-leaved coat, out of two unrelated poverties: one because the soil barely exists, the other because it has had everything stolen from it.

That is the reading Coolum leaves you with, the gradient rule set out as a single climb and stacked up one hillside: forest where the washed-down soil runs deep at the foot, wallum on the bleached sand of the plain, and hard, tight heath where the soil finally gives out on the bare rock at the top. Not a square metre of it is rich enough or sheltered enough to grow a rainforest. Read the plants as you rise and they tell you, step by step, what the ground beneath them is made of.