Exploring Kootenay Lake

There is nothing that says spring like the first guttation—not the arrival of swans, swallows, or robins, but guttation. It tells me that local plant metabolism is underway.

Guttation is often confused with dew. Although superficially similar in appearance, dew and guttation come about in different ways and are easily distinguishable. There are examples of each below.

Guttation on grass appears as rather large drops of water hanging from the tip of the blade (although sometimes a drop may slide downwards). It is formed from soil moisture that the roots have pumped upwards. During the day, this moisture would have passed out through the stomates, but with the lower nighttime temperatures, the stomates have closed. Frankly, grass is not very smart and so the roots keep pumping despite the blade having closed down for the night. The water is thus extruded from the tip of the blade to produce the guttation (from Latin, gutta meaning drop + ation).

The source of the moisture for dew is not the ground, but the atmosphere. Water vapour condenses on the cold blade. The grass (or any plant) need not be metabolizing for dew to form. Indeed, dew will form on all manner of cold surfaces. Guttation, on the other hand requires the plant to be metabolizing, making it a good sign that spring is here.

(Incidentally, one sometimes sees a picture of a spider’s web covered with droplets which the photographer has labeled as dew. Alas, those drops are formed neither as dew nor guttation, but something else.)

Nearly spherical guttation drops are hanging from the tips of the metabolizing grass.

Guttation and dew can form separately or together. The large pendulous drops near the tips of these blades are guttation; the smaller ones along the blades are dew.

The previous pictures were taken in the general direction of the Sun to attain a high contrast. There are delights to be seen in the other direction: rainbows. Typically only formed by the more nearly spherical guttation drops, the tiny portions of a rainbow are easiest to see when the drop is out of focus.

A sun dog (a parhelion) is so named because the colourful spot of light follows its master, the Sun, around the sky. Well, it follows the Sun if the cloud, in which the sun dog forms, persists. In this case, the drifting cirrus was in the proper position for maybe five minutes and then the show was over. These brightly coloured spots of light are explained by the minimum angle of deviation of sunlight refracted through the 60° prism faces of hexagonal ice crystals.

Life in mountain valleys is usually life without sun pillars.

The problem is that pillars are really striking only when the Sun is low in the sky. Around here, the Sun generally appears from (or disappears) behind a mountain and so is already too high in the sky to produce a good pillar. Yet, there are times of the year when the rising or setting Sun aligns with a valley. That is the time to watch for sun pillars.

A pillar results from the reflection of sunlight off gently tipped surfaces. Most people are familiar with seeing a sun pillar on water. If the water were calm (perfectly horizontal), only a circular image of the Sun would appear. It takes the slight tipping from small waves to drag the Sun’s image out in the vertical. A resulting pillar is seen in the lower half of the picture.

Ice crystals provide the reflecting surfaces for the formation of the pillar above the Sun. Although the majority of the clouds seen here are composed of water drops, there is an all-but-invisible veil of hexagonal-plate ice crystals falling from them. These crystals settle with their broad plate-like surfaces nearly horizontal, rather like dinner plates spread on a table. Gentle oscillations of the falling crystals provide the slight tipping needed to spread the reflected image of the Sun into the pillar seen in the upper half of the picture.

For the next short while, the Sun will be rising (for me) in this gap between the higher mountains. With luck, I may get to see more sun pillars.