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Accessibility: VERY DIFFICULT
WHAT'S HERE?
At the cabled section, J.Thomson / Out There Learning
This challenging alpine hike will take you over bare ice-carved rocks to an outstanding viewpoint looking towards Milford Sound. You will be up close to the Fiordland bedrock that is quite different from the crushed greywacke that makes up a large part of the Southern Alps further north.
LEARN ABOUT IT
Black Lake, J.Thomson / Out There Learning
This challenging alpine hike takes you to a truly spectacular viewpoint, even by Fiordland standards.
You will climb over ice sculpted and striated bedrock in a small hanging valley beside a glacier carved lake.
From the saddle looking down the valley towards Milford Sound you will see how extremely hard bedrock has allowed the ice to erode downward to create deep valleys with awe inspiring vertical walls hundreds of metres high. From the peak of the Last Glacial Maximum or LGM around 26 000 to 18 000 years ago, the ice will have retreated from the main valley and slopes about 10 000 years ago.
The bedrock is an igneous rock called Darran Leucogabbro – which is an early Cretaceous aged intrusive pluton (see below) belonging to the Median Batholith. Unlike much of the Southern Alps which are made of fractured greywacke, the Darran Mountains comprise relatively strong rocks and steep cliffs have remained long after glacial ice has melted. The mid-grey Darran Leocugabbro has an equigranular rockmass containing sparkly brown biotite crystals, small black hornblendes and white feldspar. Look also for lighter-coloured pegmatitie dykes crosscutting the rock, filling in what were once fractures in pluton. The dykes are rich in felsdpar and many have some beautiful, large (1-5 cm) crystals of hornblende.
The Darran “pluton” represents a single body of molten magma that crystallised 10-20 km deep in the earth’s crust. It likely extends over about 200 km2. It is but one of several hundred plutons that together form the Median Batholith - a 10-100 km wide belt that extends in a northerly direction right across Te Riu a Maui /Zealandia. Stewart island and Fiordland are almost entirely formed of plutons.
Such magmas likely also erupted at the surface to form volcanoes, now eroded away, that would have formed part of an ancient episode of present “Pacific ring of Fire”.
You will climb over ice sculpted and striated bedrock in a small hanging valley beside a glacier carved lake.
From the saddle looking down the valley towards Milford Sound you will see how extremely hard bedrock has allowed the ice to erode downward to create deep valleys with awe inspiring vertical walls hundreds of metres high. From the peak of the Last Glacial Maximum or LGM around 26 000 to 18 000 years ago, the ice will have retreated from the main valley and slopes about 10 000 years ago.
The bedrock is an igneous rock called Darran Leucogabbro – which is an early Cretaceous aged intrusive pluton (see below) belonging to the Median Batholith. Unlike much of the Southern Alps which are made of fractured greywacke, the Darran Mountains comprise relatively strong rocks and steep cliffs have remained long after glacial ice has melted. The mid-grey Darran Leocugabbro has an equigranular rockmass containing sparkly brown biotite crystals, small black hornblendes and white feldspar. Look also for lighter-coloured pegmatitie dykes crosscutting the rock, filling in what were once fractures in pluton. The dykes are rich in felsdpar and many have some beautiful, large (1-5 cm) crystals of hornblende.
The Darran “pluton” represents a single body of molten magma that crystallised 10-20 km deep in the earth’s crust. It likely extends over about 200 km2. It is but one of several hundred plutons that together form the Median Batholith - a 10-100 km wide belt that extends in a northerly direction right across Te Riu a Maui /Zealandia. Stewart island and Fiordland are almost entirely formed of plutons.
Such magmas likely also erupted at the surface to form volcanoes, now eroded away, that would have formed part of an ancient episode of present “Pacific ring of Fire”.
HAVE A LOOK!
Information Panel with Gertrude Valley beyond, J.Thomson / Out There Learning
Identify the classic glacial features that you will pass by, including hanging valleys, bare ice-smoothed bedrock, glacial striations, erratic boulders and huge U shaped valleys.
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Directions/Advisory
It is about a 7km round trip up to the saddle and you can expect to take between 4 to 6 hours return.
The track becomes very steep and potentially dangerously slippery in places if wet, especially on the area of rock slabs just below and around the Black Lake. Black ice (verglass) can be a problem during Autumn and late Spring, even in fine weather.There are steel cables in place to help you, but you should not attempt this route in rain or snowy conditions. After snowfall there is an avalanche hazard on this route
Google Directions
Accessibility:
VERY DIFFICULT
This track is reached from the Gertrude Valley carpark, about 98 km along the Milford Road from Te Anau.
Features
Landform
Geological Age
The glacial features are from the most recent glaciation, ending between 18,000 and 12,000 years ago. The Leucogabbro bedrock has been dated using the isotopic composition of lead and uranium in tiny crystals of zircon. The result, 137.3 Ma (million years
Zealandia Evolution Sequence
Pākihi Supergoup: 5 million years ago – present
Links