August 25, 2023
2023 Geology Group Blog 2
The Geological Story of Lake Crescent
The Earth’s surface is characterized by various landforms and features that comprise its topography. These landforms result from different geological processes that have shaped the landscape over millions of years. Erosion, weathering, volcanic activity, tectonic forces, and external factors like water and wind have all contributed to our diverse topography.
In this blog, we will consider the formation of landforms, taking Lake Crescent as an example (Figure 1).
Figure 1 Satellite photo of Lake Crescent
(From Google Earth)
Between 57 and 18 million years ago, the basalts and sedimentary rocks that formed the Olympic Mountains were deposited offshore. These were uplifted by the collision of the North American Plate and the Van de Valka Plate, forming the Olympic Mountain (Figure 2) [1].
Figure 2 North American Plate and the Van de Valka Plate
(From Wikipedia, https://ja.wikipedia.org/wiki/%E5%8C%97%E3%82%A2%E3%83%A1%E3%83%AA%E3%82%AB%E3%83%97%E3%83%AC%E3%83%BC%E3%83%88)
There are large continental ice sheets in Olympic Peninsula during the last ice age. These sheets split into two lobes when they hit the Olympic Mountains and respectively caved into the Strait of Juan de Fuca and Puget Sound.
As the glacier slides, it polishes bedrock, pushes soil, grinds up rock, and digs into the ground. This eroding process is called glaciation, which sculpts deep U-shaped valleys if the glacier moves slowly and steadily.
Figure 3 Sedimentary rocks of Lake Crescent
Lake Crescent was born of ice during the last Ice Age. Though the continental ice sheets had not hit where Lake Crescent is now, alpine glaciers eroded sedimentary rocks and carved out deep valleys (Figure 3). The deepest spot of Lake Crescent was shown to be 596 feet (182 m) (Figure 4) [2].
Figure 4 Lake Crescent Bathymetric Survey
(From Wikipedia, https://en.wikipedia.org/wiki/Lake_Crescent23/8/2023)
As the glacier retreated, water melted, and the steep valley came out. Initially, the Lake Crescent valley drained into the Indian Creek valley and then into the Elwha River [2]. About 8,000 years ago, a massive landslide originating in one of the Olympic Mountains dammed Indian Creek, which formed Lake Crescent.
The lake is surrounded by mountains that prevent other fish from entering, leaving only two species of native fish, the Beards lee and Crescenti trout [3]. On the other hand, these two species are unique to Lake Crescent because they cannot leave the lake and cannot be found anywhere else in the world [3].
The water in Lake Crescent is clear and blue (Figure 5). According to National Park Service, this is because there is very little nitrogen in the lake, and it controls the growth of phytoplankton that causes turbidity. So, in some places, we can see the bottom up to 60 feet (about 18 cm).
Figure 5 Cleanness of the Lake Crescent
This transparency and reflected light give the lake a beautiful turquoise color, creating a beautiful landscape.
Do you know what is holding back the amount of nitrogen in this lake?
To be honest, we couldn’t find any literature that indicates that this lake is low in nitrogen, and the correct answer also could not be found. However, as a hypothesis, the reason stems from the fact that this lake is a glacial lake.
In many cases, a lake is formed by water flowing from a mountain into a river. In this case, the water comes from the mountains, so it would have once passed underground and contained nutrients such as nitrogen from the soil. Moreover, these streams bring along lots of eroded soil and debris from the surrounding landscape, making the lake muddy, opposite to what Lake Crescent is like. In contrast, glacial lakes are considered to have no opportunity to obtain nutrients from the soil because most of the water does not pass underground.
In conclusion, water melting from glaciers filled the glacier-curved valley and formed Lake Crescent.
That’s the geological story of Lake Crescent.
[1] National Park Service, Geology of Olympic,
https://www.nps.gov/olym/learn/nature/geology.htm (Date: 2023/08/23)
[2] Wikipedia, Lake Crescent,
https://en.wikipedia.org/wiki/Lake_Crescent#:~:text=9%20External%20links-,Origins,and%20then%20into%20Elwha%20River. (Date: 2023/08/23)
[3] National Park Service, Lake Crescent Area Brochure
https://www.nps.gov/olym/planyourvisit/lake-crescent-area-brochure.htm (Date: 2023/08/23)
