The Terroir and Wines of the Cromwell Basin and Bannockburn
The Cromwell Basin is the most important of the Central Otago regions measured by the area under vines and there are planted intermittently along the valley for 35 kilometres although the pioneering vineyards are clustered at the southern end near the town of Cromwell. The first vineyard was planted by Olssens along Felton Road in the southern sub-region of Bannockburn in 1989.
Numerous others have followed and with the potential proven it would seem to the casual observer that it is still possible to greatly expand the area under vines particularly in the northern part of the basin.
Cromwell is a long, north east-south west trending glacially gouged basin about five kilometres wide and including the northern extension of the Lindis River valley, about 45 kilometres in length.
From the Gibbston Valley the Kawarau River runs east and joins the Clutha River at the southern end of the Cromwell basin and continues south as the Clutha River. This river has been dammed at the town of Clyde and the back up of water, Lake Dunstan, has flooded the eastern side of the Cromwell Basin and submerged the old historic town of Cromwell.
Remarkably the basin contains a range of glacial and glacial related sediments that date back from the present to 650,000 years ago. These sediments record the successive glacial advances and retreats.
Geology is a repetition of the same processes of erosion and deposition so with the Cromwell Basin we can picture during the cold cycle the glacier advancing down the Clutha Valley from the north, scouring the valley walls while a pile of rocks and rock debris is bull-dozed along at the front of the glacier.
Milder periods are marked by steams flowing from the glacier which erode and redeposit this rock debris with that from earlier periods. The onset of a warmer cycle will see the glacier retreating and perhaps melting entirely, exactly the condition of today. The initial period of rapid melting will see tumultuous flows down the rivers, cutting and eroding earlier terraces and carrying a large sediment load down the river and as the water flow weakens new terraces are formed. Then the process repeats itself and many of these cycles can be observed in the Cromwell Basin.
The valley fill sediments include till or moraine remnants, outwash gravels and fan gravels which merge into river gravels and alluvium and in the north even lake silts are preserved. All of these stages have been eroded at various times, although most of the land surface that we see today will have been sculptured by the last ice retreat. Left behind are a series of gravel to boulder terraces of various ages which form rounded hills close to the valley sides and step down through several levels to the youngest terrace which borders Lake Dunstan and further north borders the Lindis and Clutha rivers.
In the far southern section of the basin in a sub-region called Bannockburn, but also in places along the western edge of the basin, there is exposed a most interesting river, swamp and lake sediment that is much older than the glacial sediments and are dated at 15 million to 5.3 million years.
Called the Bannockburn Formation these sediments were deposited in fresh water lakes. During the long history of the formation of the Southern Alps numerous lakes and swampy depressions would have formed between mountain ranges. This particular formation being widespread suggests a more settled period that allowed swamp and lake deposits to form and at times was passive enough for swampy, plant rich deposits to become thick enough to later form lignite, a low grade of coal. This was mined in the Carrick area of Bannockburn. Considering the convulsions this mountain range has been under for tens of millions of years it is remarkable that this rock has been preserved.
It is normal for sediments like the Bannockburn rocks to form near fault lines as these are associated with the troughs that allow swamps and lakes to develop on the depressed or sinking side. Thus the western side of the Cromwell Basin is partly controlled by faulting and a valley to the east allowed the Bannockburn sediments to accumulate.
The onset of the current glacial period was gradual and in alpine areas like New Zealand probably commenced about 2.5 to two million years ago. So these sediments formed in a much warmer period and it would seem that later this same depression, a proto Cromwell Basin, still existed and allowed the developing glaciers a natural path for advancement.
The Cromwell Basin Vineyards
Vineyards are on all variety of surfaces with the plantings tending to favour the flat to rolling river terraces and outwash fans. Many growers have chosen to look for north facing slopes to maximize sunlight. As in all the South Island vineyard sites late spring frosts are the big danger.
The advances made in viticultural practises, understanding of how to extract the best flavours from each site and the general expansion of plantings is astonishing in the 16 years since the first vineyard was planted in 1989. Prior to then the river flats in the southern area supported a quite large stone fruit industry which continues though this land is currently not favoured for the growing of grapes. The rest of the country was used for sheep grazing and much of it is overgrazed and of very poor quality with paradoxically many promising areas for vineyards.
As with many South Island Rivers the Cromwell and Lindis River valleys supported for a brief period extensive alluvial gold mining between 1860 and 1900, although hard rock mining continued at the Bendigo region for many years. Today the joke is that a new period of gold mining has begun with the gold being pinot noir.
The Cromwell area is very large and while the early vineyards have been planted with the best advice it is by no means certain that the best areas have been planted yet. A great deal of development will continue for decades ahead.
Currently the vineyard owners talk about two areas; the Cromwell Basin and the smaller, attached southern region termed Bannockburn. It is better to see the region as many tiny areas of individuality that are related by climate. Hence this observer reviews separately the following regions. An average elevation is about 250 metres.
Old Cromwell Town. An old merchants shop that was removed before the old Cromwell town was flooded by Lake Dunstan and was rebuilt on higher ground.
Bannockburn and Felton Road
Many impressive wines are coming from vineyards that adjoin Felton Road, a road that runs across the southern most extension of the Cromwell Basin. The vineyards have a northerly aspect and the landscape is dissected by several small stream gullies, principally Long Gully and Pipeclay Creek, which run north east into the Kawarau River.
These vineyards lie on glacial derived pebbly terraces with the exception being some vineyards that slope up from Felton Road that are partly on sands and clays of recent age that have washed down off Bannockburn sediments (see above) and some vineyards and parts of vineyards that appear to be on sediments that are the result of gold sluicing derived from the Bannockburn alluvial gold field that lies close inland. These sloping vineyards are also on scree rubble derived from rock and sediment flowing down the hill.
This is the setting of the Mount Difficulty vineyard and the steeper Felton Road vineyards.
Much of the Felton Road and Olssens vineyards are planted on a recent alluvial fan that spreads out at the base of Long Gully and has sub soil characters that are different to the older glacially derived terraces. This fan is composed of basement schist pieces, quite angular with finer sediment layers up to 0.5 metres thick, is weakly layered and is generally unsorted. This was observed in two pits up to two metres deep that had recently been dug at Felton Road on blocks three and two.
As in many of the Otago vineyards wind blown sands that form a cap of very fine sediments over the underlying gravels are common. These are called loess.
The age of the various glacial sediments ranges from 440,000 years to recent sediments such as those associated with Long Gully. There is also an input from the Bannockburn sediments which are much older and some vineyards are planted on this formation.
The main vineyard-wineries are Felton Road, Olssens and Mount Difficulty.
Bannockburn Area. Looking north east across rubble left over from gold sluicing, across the Mount Difficulty vineyard with the Kawarau River-Lake Dunstan in the distance, then the Cromwell Basin with the Pisa Range in the far distance.
Bannockburn Area. Looking north east down an eroded gully created by gold sluicing in the 1880’s-1890’s across the Mount Difficulty vineyard with the Cromwell Basin and the Pisa Range in the far distance.
Bannockburn-Felton Road. Looking north west down and across the Felton Road vineyard with Olssens vineyard being behind the poplar trees. The Mount Difficulty vineyards are off the photo to the right. The Felton Road winery is just to the right of this picture.
Felton Road. In the vineyard and getting deep into the soil profile. The wine maker at Felton Road, Blair Walter, is wondering if I will be able to clamber back up.
The Carrick Area
Wineries and vineyards here place themselves in the Bannockburn region but are really quite removed being separated by a hill of Bannockburn sediments and are exposed on a prominent terrace adjacent to the Kawarau River-Lake Dunstan and it is makes more sense to refer to them separately.. They also do not show the complicated overlay of sediment types confused with gold sluicing as seen at Bannockburn-Felton Road.
The area is made up of one prominent alluvial, glacial terrace dated at 185,000 years and several older terraces back to 360,000 years ago. The glacial cobble beds in which the vines are planted are similar to or the same as those exposed elsewhere in the Cromwell Basin. Some vineyards are on hill slopes which suggest the vines are planted on scree from the surrounding ranges. As is also normal some areas have a surface layer of wind blown rock flour, or loess.
Wineries of interest are Carrick and Akarua.
The Western Cromwell Basin including Lowburn
The largest area of developed and potential vineyard land runs along the Western side of the Cromwell Basin and Lake Dunstan.
This is a most fascinating glacially derived landscape that can be as wide as five kilometres and which abuts against the base of the Pisa Range. It varies from simple, young flat terraces that border the lake to complex, stepped terraces that preserve the different waves of glacial advance and retreat, deep creek gullies and ravines, clumpy rounded hills of dumped glacial debris called till to glacial lake beds.
This is a rich and varied landscape of great beauty and the first time visitor to the Otago pinot regions will find out more about the landscape and the essence of what helps define the pinot by driving the back roads in this area than by endless visits to cellar doors.
The sediments in this area include Bannockburn rocks of 15 million to 5.3 million years and a small exposure of a sandy conglomerate that overlies the Bannockburn rocks and is dated at 5.3 to about 4 million years of age.
It is though the glacial sediments that are preserved in an endlessly fascinating array that are the highlight and provide the sediment-soil base for the vineyards. These vary in age from 650,000 years to the present and at least six stages of glacial advance and retreat are preserved. This of course is the glacier that advanced and retreated down the Clutha Valley from Lake Wanaka and Lake Hawea and into the Cromwell Basin. As already discussed it would appear that this basin or depression existed before the onset of this ice age so the glacier turned north and south when it entered the basin.
Most vineyards border the road that runs along the lake edge though there are plantings spreading into the inland hillier areas. These are very new so it is hard to nominate favourites though Mount Michael and Pisa Range are names to remember.
The Bendigo Gold Field Region
In the mid nineties a new vineyard area opened next to the old gold mining town of Bendigo. Here there is a favourable north facing slope that is covered with favourable glacial sediments although these are not river terrace sediments but are part of the mixed rock to rock flour debris or till that is left after a glacier retreats.
Since the pioneering vineyards on the slope new developments have moved out onto the glacial terraces and remarkably have gone much higher to slopes behind those first planted. Again these slopes are draped with glacial till. The rational of the latter is apparently to be above late season spring frosts.
Thus the vineyards of this area are developed on three different ‘terroirs’ and it will be fascinating to see what flavour differences might evolve.
A landscape highlight of this area is the remarkable semi-circular of rock debris that cloaks the bordering range of basement rocks. It is apparent that as a glacier moved down the Clutha Valley the momentum on entering the Cromwell Basin carried it straight forward pushing it high up into the range, probably a hundred metres or so, as well as turning to the south west and north east.
The glacial sediments in this area have dates from 650,000 years to more recent with the sediment cloaking the basement range being 650,000 and 450,000 years with the suggestion that in this area the 650,000 year old glacier was the most powerful as its remnant sediment is the highest in the ranges.
The winery to watch out for is Quartz Ridge. There are many other vineyards in this area.
Bendigo, Cromwell Valley. Looking south west to the vineyards of Bendigo. I am standing on boulder ‘till’ created by a glacier and left when it retreated. The vines can be seen on three different sites: those on the flat outwash plains; immediately behind is the slope up from the plain that was first planted in the mid 1990’s and started the boom in this area; and high up in the mountains the most recent plantings. An early glacier rode high up over the sites of these plantings. The white areas are bird netting to protect the grapes.
Cromwell Valley. Looking north east from Bendigo to new plantings on outwash terraces.
The Cromwell Valley from Bendigo. In the foreground is mullock from an old gold mine. New gold lies in the distance with the Bendigo vineyards in the foreground with newer plantings in the centre of the Cromwell Basin. The gap between the distant mountain ranges (the Pisa Range is to the left) is the Clutha Valley. Down this valley glaciers pushed during the cold cycles of this ice age. During particular cold spells at 650,000 years and again at 450,000 years the ice pushed high up into the ‘Bendigo Range’, not far from where this photo was taken. This glacier, possibly a hundred metres thick, entered the Cromwell Basin and spread to the south west and north east but the momentum kept some of the mass moving straight ahead, leaving till high up in the Bendigo Ranges after it receded.
Rudi Bauer of Quartz Ridge is a pioneering wine maker who opened up the Bendigo region in the mid 1990’s. Here he draws a sample of pinot noir.