I want to take some time here to appreciate the fact that there are incredible stories written within our landscapes, if only we have the eyes to read them. This is why I love the field of environmental sciences as a whole. They allow me to draw back the tapestry of the present and peak behind into the narratives of the past. Doing so reveals that Earth is a restless and dynamic system capable of tremendous activity: take for example the Manawatu region of New Zealand.
Driving through, it appears to be nothing more than your standard expanse of pastureland, maybe a few hills in there, a winding river, some small mountains in the distance, but mostly flat and grassy. Yet to comprehend the immensity of time and the multiplicity of events required to assemble these unassuming vistas is quite a task. For one thing, it wasn't long ago on a geological time scale that most of the Manawatu Region lay beneath the sea in the form of unconsolidated sediments. Its current expanse is largely due to the accumulation of these marine sediments and a progradation of the coastline. This is why it's so flat. The underlying continental crust of Zealandia isn't quite thick enough to buoy itself above sea level alone, especially as sea level today is comparatively higher than during past glacial periods.
As such, repeated marine transgressions and inundations subsequently emplaced a great thickness of mudstone, shale, limestone, marine gravels and the like. Gravel terraces are a common feature of the area but often go unrecognized because their vegetative cover or overlying layers of loess. The Massey University campus and Palmerston North itself sits atop such gravels. The Tokomaru Marine Terrace demarcates the former height of the shoreline; a huge distance inland from where it now rests.
The Manawatu River has likewise been an active agent of erosion and deposition for many thousands of years. It has incised and abandoned numerous floodplains, leaving behind another system of undulating riverine terraces. As its level rises and falls, the surrounding area feels its affects accordingly. Oxbow lakes, alluvial fans, in-filled swamps, etc. all owe their existence to this perpetual channel. The river even existence prior to the uplift of the axial ranges. These are some of the most rapidly rising topographical features in New Zealand aside from the Southern Alps. The Manawatu River, whose course crosses the ranges, has cut down through the hard greywacke rock as quickly as it has been thrust upwards to create the spectacular Manawatu Gorge.
At the top of the Ruahine and Tararua ranges, however, you'll still find those marine sediments previously mentioned. Rounded gravels, soft mudstones, etc. all compose a thin veneer draped over the more resistant greywacke. This makes the steep slopes susceptible to landslides and other mass movement failures, especially when saturated with rain. These loosened sediments are then carried away by the river to be deposited wherever it sees fit or to in-fill the coastal estuary, altering its morphology. There is even a massive dune-field associate with the Manawatu coast, the largest in New Zealand. But again, this is hidden by verdant dairy farmland
In short, what appears to be a static and perhaps even boring landscape actually carries with it a dramatic history of floods, erosion, massive uplift, marine transgression and other events that lie outside the typical human framework of cognition. With some effort we can learn to read and make sense of these events, thereby more deeply understanding our current place in things. This all stands testament to the extraordinary capacity that the Earth has for change. Nothing stays the same for long. It's the progression and interconnectivity of these processes that I find so perpetually engaging.
Of course, these ideas on dynamism can help us interpret the rest of our world even on a more human time-scale. Understanding the impermance and fluidity of life is a rather liberating experience. It is simply the nature of things, as anyone who has lived a few years can recognize. By contrast, it's often when we hold rigid expectations that things should stay the same that we do ourselves the most harm.
I just hope that this little example of the Manawatu region's geomorphology can help us all to grasp impermanence inherent in our existences. Learn to read the signs.
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