At the request of our redoubtable editor, I was going to talk about cave climates. However ... weather might be easier ...

The inimitable Samuel L Clemens - Mark Twain to you - produced Pudd'nhead Wilson's Calendar and his New Calendar in the 1890s. This was the precursor of those "Bunch of Dates" desk calendars with pithy little 'sayings of the day' - which many of you will have on your desks.

Some of Pudd'nhead Wilson's sayings include:

"Nothing so needs reforming as other people's habits."
"He is useless on top of the ground: he ought to be under it, inspiring the cabbages."
"It could be shown by facts and figures that there is no distinctively native criminal class except Congress" [Australian Government?]
"It is your human environment that makes climate." [An 1897 prediction of global warming?]
" 'Classic.' A book which people praise and don't read."

Twain's Following the Equator, published in 1898, includes a hilarious and accurate - even today - account of Australian life and mores. Try your local library.

However, one of Pudd'nhead Wilson's sayings that concerns us today is:

"Climate is what you expect, weather is what you get."

This applies beautifully for day-to-day life - and to our day-to-day interpretations of cave environments. We say repeatedly that they are stable environments and we can measure what is going on in them. There are at least three relevant parameters - temperature, amount of water in the air (humidity) and gaseous composition. The later relates mainly to the amounts of carbon dioxide and oxygen (and water vapour) in the cave atmosphere. We won't discuss gaseous composition any further in this ANDYSEZ.

Temperature is easy but most of the thermometers we use are not up to the task of measuring absolute temperatures. But a single thermometer at one site will tell you what is happening at that site - relative to yesterday, last week or whatever but not much else. More than one thermometer at different sites will tell us more. As long as you use the same thermometer over a reasonable time frame ...

Determination of the amount of water in the cave atmosphere is vitally important and extraordinarily difficult - especially with cheap and relatively available instruments. There are a number of measures of amount of water held in the atmosphere including:

• absolute humidity
• relative humidity
• saturated vapour pressure
• dewpoint

All of these are useful but all are difficult to measure - especially if there is a lot of water in the cave atmosphere (or very little - but that doesn't worry us cave mob unless we are fighting bushfires). Any or all of these measures tells us different things about the state of the cave atmosphere. More on water vapour in cave atmospheres in an upcoming ANDYSEZ.

The climate of caves is complex and, in a continent the size of Australia, together with its maritime neighbours - New Zealand and Tasmania, completely beyond the bounds of any sensible summary.

So here goes! Caves are stable environments. Nonsense! This must be qualified. What happens in Jillabenan Cave, Yarrangobilly, with one entrance is totally unlike whatever is happening in Royal Arch Cave, Chillagoe? Or in an active stream cave system like Te Anau Cave, South Island, New Zealand.

But there are some rules ... perhaps: Caves are at the mean annual temperature of the local climate. Try telling them this at Cutta Cutta or in the depths of Eagles Nest Cave, Yarrangobilly!

Caves have high humidity. Near saturation. Look at Royal Arch ... or North Glory Cave, Yarrangobilly. The first is dry because of high temperature, low humidity climates - at least seasonally. Yarrangobilly is dry because of freezing temperatures and consequent lack of water vapour in the cave atmospheres.

Caves don't change through time. We have discussed this before in ANDYSEZ 28 amongst other places. Something has changed in the lifetime of that stalagmite. What happened in the "Ice Ages"? Will the Enhanced Greenhouse Effect and the probable consequent climate change have influences on our caves and karst? What are GCMs? Do caves change from year to year, decade to decade or in millennial timescales? Obviously they do.

Keith Collin, of Green Grub Productions, provides in his fine school educational CD-ROM, a nice little diagram which likens a cave to an Esky (= Chully Bun in NZ). There is an awful lot of 'truth' in his diagram. Consider a cave insulated in a block of rock.

Sometimes we will provide lots of big entrances; sometimes just one; sometimes just a small entrance; sometimes two entrances at the same altitude, some at different altitudes. Or any and more combinations, in all sorts of conditions. A small entrance many metres below an enormous opening? But there is nearly always an enormous mass of bedrock ...

Remember that I have said on many occasions that caves can be much larger than those that we humans can enter. Water Truck Blowhole, on the way to Weebubbie Cave near Eucla on the Nullarbor, provides an interesting example. This cave is a fine example of a Nullarbor blowhole. I have visited it on many (> 15) occasions and have various photos of various ladies flying a handkerchief in the strong winds blowing out of the cave. Descend it and one finds a smallish chamber with many tiny tubes developed as a result of 'intensive phreatic preparation'. Where is all this air coming from? And all the time? And sometimes in but usually outwards?

Let's now go back to Yarrangobilly. The caves here are usually about 9-11°C. This accords fairly well with the general wisdom about altitude, latitude, climatic regime and so on. Why then, deep in Eagles Nest Cave at Hughies Dig, is there a passage labelled, on the wall in candle or carbide smoke, as "Fuck its Cold" - the year round temperature is about 40°C. Some parts of Eagles Nest are markedly affected by cold air drainage and ice development in autumn and winter. But why is Hughies Dig so very cold all the year round. Part of this will be due to evaporative air conditioning effects. Part may be produced by the Joule-Thompson effect.

I look forward to explanations of the Joule-Thompson effect from my readers in the next Journal. Might indicate that somebody reads this stuff.

Let's now go to Jenolan (although these effects can be seen elsewhere - Jersey Cave at Yarrangobilly occasionally behaves like this - and probably very many other temperate climate caves). Some of those who visit Lucas Cave wear glasses. As we march along the passage suddenly our glasses fog up! We walk back a few metres and we can see through our glasses again.

What is happening? We have a very complex relationship between cave geometry, temperature, water content of the air (which is not necessarily the same as relative humidity) and barometric pressure all influencing the density of the cave atmosphere and the conditions under which water is deposited from the atmosphere. Water deposited from the atmosphere = glasses fogging! Temperature changes the density of air; moisture content changes the density of air; barometric pressure influences temperature, volume and density. Ernie Holland has termed these transitional areas as 'thermoclines' but I suspect that we are not dealing with just temperature differences. But investigation of this simple, but complex and commonly encountered phenomenon, are needed but not necessary easy.

Lots of questions here and some contentious ideas exist in this field so we will explore cave climates more fully later. Perhaps even another guest ANDYSEZ.