Pangeo Education took some of our explorers out for a longer overnight trip to explore the canyons around Yakima, Washington. The geology around Yakima is amazing, with lots of carved canyons, showing off interesting rocks, and many examples of weathering and erosion. The life in those canyons is also really amazing, with many plants and animals adapted to living in the harsh shrub-steppe habitat. Our explorers were on the look out for strange rocks and interesting critters.
We first stopped at Umtanum Canyon, a beautiful canyon carved by Umtanum Creek, which flows into the Yakima River. In this area of shrub-steppe habitat, the hill tops are usually treeless grasslands (steppe), with just a few shrubs such as sagebrush and rabbitbush. In the canyon bottoms, next to water, there are some trees like aspen, cottonwood, and alder. The shrub-steppe habitat is also special because it can be very hot in summer, and very cold in winter. So, the plants and animals have to adapt to this. Our first task was to think about how animals adapt to extreme temperatures.
How do animals adapt to extreme temperatures?
We started by thinking about one of the animals that Umtanum is famous for, but we likely wouldn’t see on such a cold day. Can you guess what animal might like a hot dry place, but we won’t be able to see when it’s cold? Rattlesnakes! In the spring and summer we have to be super careful in Umtanum to watch out for rattlesnakes, but not in the fall and winter. Snakes, like other reptiles, are ectothermic (ecto means outside and thermic means heat). Where do they get the heat to keep their bodies warm? From the outside, from the sun and warm air. So, when it’s below 60 degrees they hide in dens called “hibernacula” where they hibernate until it is warm enough. Actually, snakes also have to hide in the shade or underground when it’s too hot too! So, rattlesnakes, adapt to the extreme temperatures by hibernating.
How do birds deal with extreme temperatures though, do they hibernate? No, birds have adaptations they allow them to leave if the temperatures are too extreme, what are those adaptations? WINGS! They can just fly away to a better place! However, many birds live in Umtanum Canyon even when it’s super cold. Birds are endothermic (endo means inside and thermic means heat). What helps keep their bodies warm even when it’s cold? Feathers! Feathers are like fur and they trap lots of heat, keeping birds warm all the time.
As we wandered up the canyon, following Umtanum Creek, we noticed part of the trail, right next to the creek, was falling into the creek. We stopped to look down the cliff, and figure out why the trail was being eaten away. The little cliff was about 6 feet high, and was made up of lots of smooth, round rocks, buried in sand. Why was the cliff falling away and why were the rocks inside the ground?
Our explorers quickly figured out that the creek was slowly cutting into the cliff, eating away the bottom, and making the dirt and rocks above fall down. Then one of the explorers asked, “Why are there rocks in the dirt though? Where did they come from?”. We looked around. There were no big rocks nearby, except way up on the cliff. “They must have rolled down from the cliff.” an explorer suggested. “But they are smooth and round and the ones from the cliff are sharp, and not round. They actually look like river rocks. Which means the river put them there”, another explored observed. “So, the river use to be bigger and higher, and buried the rocks, and now the river is eating down through the old river bed.” another explorer explained.
And they were both right! Those rocks had been knocked of the cliff, further up the canyon, and then slowly smoothed and rounded by the river. They were then deposited at the bottom of the old river bed, which is now being eaten away by the current creek. That is weathering and erosion! The river rocks being smoothed by the water and hitting other rocks in the river, is weathering. Weathering is when rocks are changed by wind, water, chemicals, temperature, plants, animals, and other processes. The rocks and soil falling down the cliff and being moved by the river, is erosion. Erosion is when weathered rocks and soil are moved by forces, usually water, to another place.
Further along the trail, also right next to the creek, we found some evidence of an animal that causes weathering and erosion. Next to the trail were several big branches, with all the small branches gone. As we looked around, we found many aspen stumps, that didn’t look like they had been chopped down with an ax. They looked like they had been “chomped down” by a beaver. Then we noticed trails led through the grass from the stumps, to the creek. In the creek were lots of branches and logs, the beavers had placed, to make small dams. Those dams will change how the creek flows, causing more or less erosion in different parts of the river. Beavers are adapted to changing their environments so they can get more food from the flooded creeks. Their favorite foods, such as young trees and grasses grow along their flooded ponds.
The canyon has human history too. The Yakama people used to live here. Later, there was an old homestead here, and the evidence left behind are apple, walnut, and pear trees. Autumn is the perfect time for apples. We found trees with several different kinds of apples. Some of us liked the big red ones while other explorers liked the small sweet and tart yellow ones.
Finally, on our way back, while snacking on apples, we found a huge rock in the middle of the path, that had been split. How could such a big rock break like this? Did it break when it was rolling down the hill? If so, would it have broken perfectly in its resting place. No, it had to have broken in this spot. Whatever broke it was gone? What could break a boulder, but disappear completely? Maybe it was ice! Freeze-thaw weathering is when water gets into the cracks in a rock, and then it freezes. Water is one of the only liquids that expands as it gets cold; most liquids shrink when the freeze. So, what happens when the water inside the cracks in the rock freezes? The rocks break. In places that freeze, this is one of the main types of weathering. In Part 2, we will find even more evidence of freeze-thaw weathering, as well as many other kinds of weathering.
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