FOX AND FRANZ JOSEF GLACIERS,
NEW ZEALAND.

Two big New Zealand Glaciers, in Westland National Park transport ice from the high alps, down steep valleys. The glacial flow is unusually fast as the ice creeps and tumbles down the steep ravine and the glaciers reach remarkably low altitudes. Glacial ice reaching into a forest is unusual in temperate climates, including New Zealand, where glaciers are normally confined to mountain peaks. Mountain glaciers generally either melt, or crash as avalanches, while still far above the vegetation limit.

Franz Josef Glacier

Fox Glacier Panorama

(Panorama Photography by John Wattie)

The panoramas you will see here show New Zealand's highest mountains. They are crumbling away. Glaciers are carving them right now.

Foot hills beside the mountains have been smoothed by glaciers during the recent ice ages. Rock debris carried away from the mountains by ice and subsequently by rivers, has left vast shingle plains. Also heaps of rocks called moraines and other glacial landforms you will shortly see at this URL. The top layer of shingle has been covered by wind-blown glacial dust (loess) to make soil.

(Those taking the quick South Island Tour through the web site have already seen a cross section of glacial outwash gravels at the Rakaia Gorge).

A visit to the Fox and Franz Josef glaciers gives a good understanding of erosion by moving ice because it is happening right now, near sea level, accessible to the unfit, at a comfortable temperature, close to excellent accommodation and tourist buses.

The Southern Alps of New Zealand are elevated by tectonic compression along the alpine fault. The mountains are basically compressed ocean sediment (greywacke rock), only partially converted by heat and pressure in the earth's crust into slightly stronger schist. This soft, crumbly rock is easily smashed, by water freezing and expanding in the cracks. The Fiordland Mountains of New Zealand are made of tougher rock and the glacial landscape there is rather better preserved because of that - as we will eventually see on this site.

Franz Josef Glacier

Franz Josef glacier, like all the world's ice rivers, has receded considerably since first recorded, due to global warming after the little ice age ended around 250 years ago in New Zealand. The little ice age duration was different in different contries and is well documented from human records here.

When first explored by Europeans, (A.P. Harper and Charlie Douglas, 1865), the glacier was probably at a new peak after the little ice age.

There is a lag period between changes in climate and position of the glacier's terminal, because ice flow is slow. The lag is shorter than usual for Franz Josef and Fox glaciers because their ice flows so fast down steep, narrow valleys they quickly respond to two processes which determine their length:

Snow fall in the Southern Alps versus

Melting at the terminal face.

Glacier surges can be superimposed on these 2 basic processes, but are only seen to a small extent in New Zealand. A sudden advance of a glacier may be started by melting in the ground under the glacier, which is often rock debris (till) and water channels in the glacier quickly drain. The ice lurches forward on its water-lubricated base. Ice lower down often cumples as it pushes the terminal forward. Crumpling shows up well on aerial photographs after a surge. The compacted snow in the source region is partially drained (often from an ice cap, as in Iceland, rather than a sloping plateau, as in the Southern Alps). After a surge, the glacier retreats, only to surge again when more snow collects high in the accumulation zone. Quick surges (days to months) are recorded in Alaska while slow surges (years) are noted in Svalbard. (The difference between a slow surge and a glacial advance may seem a bit subtle, but a surge depletes the collection zone from below, while an advance results from extra snow accumulating and pushing the glacier terminal further down.)

New Zealand ice ages probably coincide with Northern Hemisphere ice ages, but have different names. During the last Pleistocene ice age here (Otiran) these valley glaciers became piedmont glaciers and reached into the Tasman Ocean. Each ice age was split into periods of advance and retreat, which continue to this day, which makes some geologists claim we are even now in the warm phase of an ice age.

The first description of the two huge glaciers was from the sea in 1859, the famous mariners Tasman and Cook both missing them earlier. From the log of the brig Mary Louisa (Francis and Young):

"... an immense field of ice, entirely filling up the valley formed by the spurs of the twin peaks and running far down into the low land."

Glacial Advance and Retreat

Franz Josef Ice Retreat by Thomas Riker and John Wattie

Animation of Franz Josef Ice Retreat:
original idea by Thomas Riker of Austria,
base picture from US geological survey but considerably "cleaned up" and gif animation by John Wattie.

Graph of glacier retreat and temporary advances
from US geological survey

jökulhlaup is a sudden flood from a glacier caused by an ice dam collapsing.

1867 (T. Pringle, first known photograph of Franz Josef Glacier)

circa 1939

Franz Josef Glacier, 1951
1951

1952

1960

Franz Josef Glacier, 1964
1964 (photographers unknown).

1994 Large photographs of the terminal face of Franz Josef Glacier: press here

Text and colour photographs by John Wattie

A rapid advance in December 1965 was caused by heavy rain, which percolated through crevasses and lubricated the base of the glacier, by breaking the frozen bonds between ice and rock. A flood of water and ice headed down the valley but fortunately nobody was injured. Unlike some glaciers, surges are not a regular feature in New Zealand.

The retreating ice uncovers glacier-smoothed rocks on the valley wall, with no vegetation. Weathering of the rock creates soil. As the bush grows back, young forest is seen next to more mature trees and the junction is called a trim line. These trim lines are common in glacier country and mark previous advances of the ice.

A well marked trim line lies well above the 1951 glacier surface, dated as the 1907 line by geologists. Above it is the 1865 trim line, pretty much where the 1867 photograph shows the ice surface. Growth of vegetation means the 1867 trim line was more easily seen in 1951 than in 2000.

There is also a ledge at the 1867 line, seemingly matched by another on the opposite wall, which is probably trough in trough formation. Ledges can also come from lateral moraine and this is explained at Fox Glacier.

The 1867 photograph shows ice surging around sentinel rock on the right. Subsequent photographs are taken from the top of this rock.

From 1939 to 1949 a lake lay below the terminus, dammed by ice at the 1860's terminal moraine. Boating on the lake was popular, but gradually it became more shallow as the glacier dumped more rocks into it. Suddenly a block of ice on the lake floor dumped its rock ballast and erupted through the lake surface, which discouraged further navigation. The lake drained when ice in the terminal moraine melted. The moraine rocks were washed away to leave the gravel outflow through which the river currently flows.

Terminal moraines are frequently washed away in Westland because the rivers are not only fed by glacier melting. Heavy snow on the peaks becomes heavy rain at lower, warmer altitudes, producing high water flow both under and over the glacial ice.

The 2000 picture from Sentinel Rock shows the terminus has advanced again during the 1990's. The average temperature in New Zealand has not fallen. The advance is due to greater snow-fall in the mountains and is only temporary. Because the glacier valley is so steep, changes in climate affect Franz Josef rapidly, with about a 5 year delay between snow on the tops and advance at the foot of the glacier.

2000 (John Wattie)

2002 - the ice is retreating again.

2006 - the ice is advancing and is further down the valley than in 2000

2006 (John Wattie)

Notice how the rock projecting from the valley wall on the left of the picture has been smoothed and ground by the glacier, which covered it 50 years ago, and for many centuries before that. Longitudinal grooves in the rock are characteristic of glacial carving. Vegetation has begun to cover it now and the grooves are harder to see than in 1964.