GeoSphere

Bubbling Merrily: Artesian Springs

Matt Herod December 7, 2015

Click here to display content from www.youtube.com

Always display content from www.youtube.com

I recorded the video above on a recent field camp near Deep River, Ontario. This video shows a great example of a flowing artesian spring which is bubbling up at the headwaters of a creek. The water is freezing, crystal clear and totally delicious! The classic textbook on groundwater, Freeze and Cherry, puts the attraction of groundwater springs nicely when they say “Flowing wells (along with springs and geysers) symbolize the presence and mystery of subsurface water, and as such they have always evoked considerable public interest.”

There are two types of artesian springs. Those that are controlled geologically, which are commonly taught as the only variety of artesian system, and topographically, which are often overlooked.

Geologically controlled artesian springs/wells result from a specific combination of hydrogeologic conditions. Specifically, the aquifer must be under pressure, which is usually caused by a steep elevation gradient in combination with relatively impermeable confining layers such as clay. This is called a confined aquifer. Recharge to this aquifer occurs on top of a hill, where the aquifer outcrops. This water then infiltrates through the permeable sediments to the water table and into the confined aquifer. However, this does not explain why a spring or a well drilled into and artesian aquifer often bubbles up with water, like the video above.

A conceptual model of a confined artesian aquifer in which the recharge area is exposed at higher elevation and the aquifer sediments are bounded by two aquitards. Source

The reason for this is somewhat abstract and has to do with water pressure. In an unconfined aquifer the water table and the potentiometric surface, which is the abstract line dictated by the water level in the well, are generally synonymous and are defined by the point at which the water pressure is equal to atmospheric pressure. However, in confined aquifers where artesian conditions exist this becomes more complicated. The reason for this is that within the confined aquifer the water pressure is often greater than atmospheric. Imagine diving down in a lake and feeling the pressure of the water above you. Therefore, when this aquifer is drilled or a pathway to conduct water to the surface exists the water will want to flow upward towards that point where the water pressure and the atmospheric pressure are equal. This point can be above the ground surface and this leads to flowing artesian conditions. The figure below illustrates this concept nicely.

Source: Minnesota Department of Health,

In this figure the water level in the well on the right, which is connected to the confined aquifer, is distinct from the water table in the unconfined aquifer. The water is not flowing because the potentiometric surface is not higher than the ground level. In the other artesian well, which is flowing, the water flows up to the potentiometric surface, well above the ground surface. This is because that surface represents the point where the water pressure, which is the pressure of the water within the confined aquifer, and the atmospheric pressure are equal.

The other type of artesian spring are topographically controlled and often occur in valleys. The reason for this is that as water recharges at the top of hills this can locally raise the potentiometric surface if there is a steep valley nearby. Therefore, at the base of the valley the potentiometric surface can be higher than the ground surface causing water to discharge.

So which type is the one in the video? Let’s start by checking the topo map of the region. The spring is located at the red star, which based on the terrain map is actually pretty flat, certainly much flatter than the opposite bank of the Ottawa river.

Based on this map it doesn’t look like the spring is topographically controlled. There may be some local elevation that does not show up at the map scale, although I don’t recall there being that much. One thing to keep in mind about this location is that there is a lot of bedrock exposed. It is possible that some of this bedrock aquifer is over-pressured and water flowing through fractures in the bedrock is discharging as a flowing artesian spring. In my mind, after about 10 minutes of looking around, this is the most likely scenario. It may also be completely wrong, but without a more detailed look around it is difficult to say.

Artesian springs and springs in general really represent the importance of protecting our groundwater resources. It is critical that places such as this artesian spring be protected from contamination and development as they are very fragile and represent important sources of clean, safe water as well as habitat to a large diversity of local flora and fauna. If you know of any artesian springs in your area please comment below and let me know if they are protected or if they have been compromised by contamination or development.

Matt

p.s. I’ve teamed up with Science Borealis, Dr. Paige Jarreau from Louisiana State University and 20 other Canadian science bloggers, to conduct a broad survey of Canadian science blog readers. Together we are trying to find out who reads science blogs in Canada, where they come from, whether Canadian-specific content is important to them and where they go for trustworthy, accurate science news and information. Your feedback will also help me learn more about my own blog readers.

It only take 5 minutes to complete the survey. Begin here: http://bit.ly/ScienceBorealisSurvey

If you complete the survey you will be entered to win one of eleven prizes! A $50 Chapters Gift Card, a $20 surprise gift card, 3 Science Borealis T-shirts and 6 Surprise Gifts! PLUS everyone who completes the survey will receive a free hi-resolution science photograph from Paige’s Photography!

My DEFENCE! Follow live tweets with #129I @ 2:30pm ET

Matt Herod November 16, 2015

My PhD defence is this week (Wednesday) at 2:30pm ET. I am feeling pretty good about the whole thing but at the same time nervous. I just don’t know exactly what to expect. I have a sort of idea of what the questions might cover and where my assumptions or conclusions might be challenged. However, the uncertainty of all this is what is making me nervous.

Credit: XKCD

I have gotten lots of good advice from people such as “you are the real expert on the material” and “be confident and prepare a great talk”. All of this is great advice, however it doesn’t really help assuage the feeling that this is the most important talk I have ever given and the nerves that accompany that. Furthermore, despite the fact that I am now an expert on 129I I still have to convince four very smart people that I what I did was worthwhile and good science.

As far as my preparations go I have read lots of articles from fellow bloggers about how to prepare and what to think about and talked to postdocs in the lab. These have all been very helpful things to do, but at the end of the day I know that I will be the one standing at the front of the room and facing the steely gaze of the examiners (not really, they are all nice people). I have read over my thesis several times, prepared a list of possible questions, re-read key articles and reviewed the basic principles of the models I used and the statistical tests. I still feel unprepared and I doubt that feeling will go away until I start my talk. Plus, thesis committees are still scary!

Credit: PhD Comics

Anyway, in the interest of distracting myself yet also being sort of productive I am preparing to live-tweet my defence. I am pre-scheduling about 20-30 tweets for the time during my talk so you can view these key points of my thesis as I talk about them at uOttawa. Follow the feed with #129I. Interact with the tweets, ask questions, etc. I won’t get to them until later in the day…or maybe the next day, but I will eventually.

Wish me luck and remember, follow #129I!!!! Tweets start at 2:30pm ET.

Also, I’m using a new presentation program called SlideDog. I mean why not try something new for the most important talk of my life. Stay tuned for this:

Credit: PhD Comics

Photo of the Week #50

Matt Herod November 6, 2015

This week’s photo is brought to you from outer space! Indeed, this a beautiful cut section of a meteorite that fell in northwest Australia and was found in 1892 (ignore the label behind it). It is an iron-nickel meteorite and is composed entirely of metal. This crazy cross-hatching, which is most commonly found in such iron-nickel meteorites, is called a Widmanstätten pattern.

Widmanstätten patterns, also known as Thomson patterns, are revealed only when the meteorite is cut, polished and acid etched. The patterns formed when the meteorite cooled and only do so if the meteorite cooled very slowly i.e. over millions of years.

First, when the meteorite is hot the entire thing is mono-crystalline and is formed of an Fe-Ni phase called taenite. However, as a it cools another phase develops called kamacite (low Ni) which grows within the existing taneite (high Ni) lattice resulting in the Widmanstätten pattern.

Iron meteorite found in Roeburne, Hammersley Range, NW Australia. This piece is exhibited in the Museum Reich der Kristalle, Munich, Germany by Konstantinos Kourtidis

From the GeoSphere Archives: The Wooden Wall

Matt Herod November 5, 2015

It is once again time to write about geology and classics and the incredibly important impact the geosciences had on the ancients and their way of life. My previous post on this topic can be found at my old blog location as the post: The Odyssey and Geology. I’ll begin by relating a story:

Themistocles (Wikimedia Commons)

The two fleets, the Persians the the Greeks, which was composed of the navies of all the city states, but mainly Athens, met in the narrow Strait of Salamis for a final and deciding battle. The Persian king, Xerxes, was so certain of victory that he set up a throne in nearby Athens to watch the battle. The true architect of the battle though was not Xerxes, but the Athenian Themistocles, a politician and general. Indeed, it had been Themistocles who had convinced the Athenians to build a navy of over 200 additional ships in the years prior to the war and it was he who stationed the Greek navy in the Strait of Salamis, which was advantageous for the smaller Greek navy. The battle proceeded according to Themistocles’ plan and the Greeks were able to out-maneuver the Persians in the narrow strait and succeeded in decimating the Persian navy. This was a great blow to Xerxes who fled back to Persia with much of his army. The next year the Greeks were able to defeat the remainder of the Persian army driving them out of Greece and winning the war. Salamis was the turning point of the war and saved Greece from certain doom.In 480 BC the ancient Greeks were faced with their biggest threat in history: the invasion of the Persian king, Xerxes and his armies. The Greeks, despite being horribly outnumbered had fought bravely but been defeated in the Battle of Thermopylae. The Persians then advanced through Greece nearly unchecked and conquered Athens. However, the Persians knew that to fully conquer Greece they would have to do so at sea as well as on land. Things were looking pretty grim for the future of ancient Greece at this point.

Source: Wikimedia Commons

The hero of Salamis, Themistocles was a very persuasive politician as well as tactician. In fact, it was he who convinced the Athenians to build the 200 triremes (ships) that made of up the bulk of the Greek navy and can be credited with saving Greece. The credit cannot be only given to Themistocles though. In fact, the idea came from the Oracle of Delphi. The Greeks were very worried about the impending Persian invasion and decided to consult the oracle for advice on how to win the war. The oracle cryptically answered along the lines of the “wooden wall will save you”. Clearly, this answer could not refer to the building of an actual wooden wall since that would be stupid and obviously could burn down. Themistocles interpreted the oracles advice to mean build a navy. Unfortunately, the ancient Greeks had the same problem with national defence requisitions as governments do today and money for such a venture was not easily at hand. However, geology was going to come to the Greeks rescue in the form of a major silver discovery at Laurium, a small mining community just south of Athens, providing the Athenians with enough money to afford a new navy. Without the discovery at Laurium it is possible the navy would never have been built and ancient Greece would have fallen into Xerxes hands. Ergo, geology saved ancient Greece from total domination by the Persian empire.

So now what about Laurium?

Miners in Laurium. They were all slaves. (Source: Wikimedia Commons)

Google Maps

The Laurium silver mines are located just south of Athens and are world renowned for the excellent mineral samples the area still produces in addition to its storied past. The mineralization is of lead, zinc and silver and is associated with the emplacement of an igneous body within metamorphosed sediments. The ore occurs mainly within marble especially at the contact with other metamorphic or igneous rocks (www.mindat.org). The list of minerals found in the Laurium mining district is a mile long and it is actually the type locality for about a dozen minerals as well, making it a world class mineralogical site. The mineral Laurionite is named in honour of the location. In addition to the minerals occurring in the mines there are a host of others that occur in the ancient slag piles left by the Greeks. The slag has reacted with the sea water used in processing the ore in ancient times to produce a suite of new and unusual minerals there as well.

Agardite, Laurium, Greece (Source: www.mineral-forum.net – Used with permission)

Diaboleite, Laurium, Greece (Source: www.mineral-forum.net – Used with permission)

Conichalite, Laurium, Greece (Source: www.mineral-forum.net – Used with permission)

Nealite, Laurium, Greece (Source: www.mineral-forum.net – Used with permission)

Annabergite. Larrium, Greece. (Source: www.mineral-forum.net – Used with permission)

The ancient ore processing techniques of the Greeks were obviously primitive relative to today’s, however, they were still able to extract both lead and silver from the ore. The process essentially involved numerous washes with water in a sloped basin. The heaviest material was collected and smelted, and the resulting slag was carted away and dumped. Since then the slag has had a few thousand years to oxidize and this process has resulted in the growth of all sorts of interesting minerals like the ones pictured above. Laurium is still geologically relevant today from the perspective of the mineralogist or mineral collector as the area still produces some world class specimens.

It has always amazed me how deeply geology is integrated with our lives today, what with our dependence on natural resources for nearly everything. However, it would appear that this is not a new phenomenon and that geology always has been and will always be a crucial part of our lives.

Thanks for reading!

Matt