Weathering in Milford Sound
Tasks:
- What types of weathering can you observe on the fjord walls? Describe at least two examples.
- How does Fiordland’s humid climate influence the weathering process?
- Do you notice differences between the rocks near the water and those higher up? What could be the reason?
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Milford Sound is one of New Zealand’s most breathtaking natural wonders. The nearly vertical fjord walls rise up to 1,200 meters above the water and have been shaped over millions of years by geological processes. One of the key forces transforming this landscape is weathering – the natural breakdown of rock through physical, chemical, and biological processes.
Fiordland’s humid climate, with extremely high rainfall, significantly accelerates weathering. In this EarthCache, you will learn about these processes and observe their effects firsthand.
What is Weathering?
Weathering is the process by which rocks break down due to natural influences. There are three main types of weathering:
A) Physical Weathering (Mechanical Breakdown)
- Frost Wedging: Water seeps into cracks in the rock, freezes, and expands, causing the cracks to grow and the rock to fracture.
- Thermal Expansion: Large temperature fluctuations cause rocks to expand during the day and contract at night, leading to stress and fractures.
- Pressure Release: When glaciers melt or rock layers erode, the reduced pressure allows underlying rocks to crack.
B) Chemical Weathering (Dissolution and Transformation of Minerals)
- Acidic Weathering: Rainwater can be slightly acidic and dissolve certain minerals in the rock.
- Hydration: Minerals absorb water, swell, and weaken the rock structure.
- Oxidation: Oxygen reacts with minerals such as iron, leading to rust formation and rock decay.
C) Biological Weathering (Influence of Plants and Animals)
- Root Wedging: Plants grow in rock crevices, exerting pressure and enlarging cracks.
- Microorganisms: Mosses and lichens release acids that chemically break down rocks.
- Animals: Birds and other animals nesting in rock crevices can loosen material.
Weathering in Milford Sound
Milford Sound is one of the wettest places on Earth, receiving over 6,000 mm of rainfall annually. The water cascading down the fjord walls in countless waterfalls significantly enhances weathering. Here, you can observe common signs of weathering:
- Large boulders that have broken off due to frost wedging or root wedging.
- Rough, eroded rock surfaces affected by chemical weathering.
- Plants growing in small cracks, slowly breaking down the rock.
- Color changes due to oxidation or chemical reactions.
https://en.wikipedia.org/wiki/Weathering
https://de.wikipedia.org/wiki/Milford_Sound/Piopiotahi
https://www.mineralienatlas.de/lexikon/index.php/Verwitterung