Monday, April 13th - Tuesday April 21st
What do I need to complete?
- Read this webpage noteset
- Watch all video links and observe all photo links and examples
- Read Chemical Weathering Section in Earth Science Review Book (within Ch. 4)
- Complete Weathering Rates Assignment and submit via MS Teams
- Join in MS Teams "Earth Science Live" video conference Monday, April 20th at 10am (I will summarize what we have learned so far in this unit, discuss this unit going forward and seek advice and have conversation on how the online learning experience has been for you so far. I will send out a Remind Text two times before that to "remind" you about the meeting.
Summary of Physical Weathering of Rock
Last section detailed the physical (or mechanical) breakup of rock into smaller pieces. Nature does this in a variety of ways. Rocks heat up and cool down daily and seasonally with temperature changes, causing rocks to expand and contract and weaken them to break apart. Rocks also have water seep into cracks, and in places that get below freezing often (like New York State), that water freezes, expands, and fractures the rock apart. Areas on Earth with trees and grasses have roots grow into the bedrock and break it apart as the tree and grass matures and grows, enlarging the rock cracks and breaking it apart. In desert areas, wind blows sand around causing the sandblasting of rock (called abrasion) which breaks tiny fragments off (creating more sand!!) and wearing rock away. In your noteset these were:
1. Exfoliation 2. Frost Action 3. Root Action and 4. Abrasion
If you have seen the movie "The Martian" with Matt Damon, think about what type of weathering primarily happens on the surface of Mars? What climate area on Earth is Mars most similar to?
New Material -Chemical Weathering of Rock
On Earth, rock is not only broken down physically but rock often gets soaking wet, and water helps to weaken and break rock apart too. Chemical Weathering occurs when water, combined with weak acids works to dissolve rock by chemical reactions. This differs from physical weathering in that no chemical reaction takes place with physical weathering, the rock is simply broken apart into sediment. A useful analogy can be to consider a sugar cube or alka seltzer tablet or even the dye tablets used to color Easter Eggs. Physical weathering would be to just break it in pieces with your hands. Chemical weathering would be to drop it in water or vinegar and dissolve it. In that case, a chemical reaction occurs and the tablet, or rock "disappears". It actually just turns into what we call dissolved minerals, which is essentially like mineral water or what you may have heard called "hard water", common in rural areas where many homes have water wells.
Before we get into details and videos on chemical weathering, it is important to note when and where it takes place on Earth. Can chemical weathering happen in the Sahara Desert of Africa? Think about what is needed for chemical weathering. Water!! So chemical weathering does not happen in deserts, places like Phoenix, Arizona or Death Valley, California or the Atacama Desert in South America where one weather station has not reported any rain since the 1950's!!!!
So where on Earth then do you think the most chemical weathering takes place? If you are imagining rain forests, you would be correct! There are a couple of reasons for this. First of all, with no cold season, it can rain, and rock can be wet all year long. This will result in near constant dissolving of the rock because it just doesn't get the chance to dry out. So places like the Amazon Rain forest in Brazil, Congo Rain forest in Cental Africa, and the rain forests of Indonesia have the most chemical weathering on Earth. But chemical weathering can happen here in Buffalo too. When?
Well to answer that question, we know that water is needed, so anytime of year from about March through Novemeber can have chemical weathering. But the other factor at play is the speed of the chemical reactions. A rock soaked with water this 35 degrees Fahrenheit is not going to dissolve too fast. Think back to an experiment that you hopefully performed at some point in middle school. If you drop a sugar cube (or any tablet that dissolves) in scalding hot water (150 deg F) versus ice cold water (33 deg F), what will be the difference in how fast the tablet dissolves? (By the way, most hot water tanks in a home for example heat water to about 120-130 degrees Fahrenheit, hot tubs are usually about 100-102 deg F, and pure water freezes at 32 deg F)
If you recall that the tablet will dissolve really fast in hot water and take a few minutes to dissolve in very cold water, you would be correct. The faster moving molecules in hot water help to dissolve the tablet quicker just like a faster moving construction crew could demo a kitchen faster than a slow moving crew. So what does this have to do with chemical weathering? It occurs faster in warmer climates where it is rainy!!!! So in Western New York, we really only have chemical weathering dissolving our rock on warm rainy days in May through October for the most part. So it is not a real important process for the breakdown of rock in our part of the world. South Florida near Miami? They get tropical rains much of the year and it is almost always at least 80 degrees there, so chemical weathering is going to dissolve the rock there nearly all year long.
The noteset has a few examples of the different specific types of chemical weathering, but do not spend time memorizing those. It is more important and interesting to see the types of features that form from chemical weathering! To follow along in the notes on P. 3-4 though, the notes mention Carbonation, Hydration, Oxidation (rusting), Plant Acids, and Acid Rain in that order.
B. Chemical Weathering
1. Carbonation reacts on limestone, marble, and any other rock with calcite or dolomite in it. In Western New York, we have limestone bedrock in some towns like Cheektowaga and Clarence, and so this is an applicable example. However, we do not have any caverns like some other places in the country that you will explore with the links below. Those caverns can form:
4. stalagmites (sounds like mice, which crawl around on the ground is one way to remember the difference)
In Kentucky, a state famous for its limestone bedrock and famous caverns also has the national Corvette Museum. In 2014, a sinkhole formed when an unknown underground cavern had its ceiling collapse. It took with it about 6 rare (and expensive) classic corvettes shown being hoisted back up in the picture here. Luckily, no one was injured as it happened overnight.
Florida is the state with the most sinkholes however, as it has strong chemical weathering all year and has limestone bedrock under almost the entire state. Each blue dot on the map below is a known sinkhole.
Although it came out a bit fuzzy, the image below shows hundreds of ponds/lakes in central Florida that are actually sinkholes. Notice them around Orlando (and Disney World) in the northern part of the image and then also a large cluster near Winterhaven near the bottom of the image. Feel free to look around yourself on Google Earth, just zoom in to Orlando, Florida.
A few of you may have been to Howe Caverns (New York State over near Albany, 4 hr drive), Mammoth Caves, Kentucky (about 8 hour drive) or the largest in North America, Carlsbad Caverns in New Mexico (probably a 30 hour drive in case you were curious!) Caverns have been a place of residence and a tourist attraction for all of human history. Watch the short video below from YouTube, a tourism video of Carlsbad Caverns to see some great imagery and explantation of how they form.
After watching, I have just a couple of things to add. The process of forming a cavern that large we suspect takes hundreds of thousands of years. The process of weak sulfuric or carbonic acid dissolving rock is not as quick as a tablet or salt or sugar dissolving in water. If you placed a piece of limestone for example in class into a cup of weak acid, it would take years, not minutes for it to dissolve. Second, there are some places in the world with even more massive caverns such as in Mexico and in Cambodia and Vietnam (both in Southeast Asia). Some in wetter environments are completely filled with water, as you might expect. The following beautiful video shows another way to explore these massive caverns.
Howe Caverns in New York is a bit of both. It is partially filled with water, so you can walk around in the cavern about 400 feet underground, and then get in a small boat and paddle around an underground lake in complete darkness when they flip the lights off. I was there once it was pretty neat!
Next, move on to the next web infopage Weathering Rates, P 5 in your noteset and then complete the assignment "Weathering Rates" posted on MS Teams.