What is a tidal pool?
A tidal pool, also commonly called a tide pool or rock pool is water left behind when the ocean recedes at low tide. Tidal pools can be large or small, deep or shallow. Tidal pools are very dependent on tides; they are formed in depressions along the shoreline and are filled with seawater that gets trapped as the tide recedes. They typically range from mere inches to a few feet deep.
What are tides?
A tide is the alternating advance and retreat of seawater along a shoreline. When the water reaches its greatest extent along the shoreline, it is said to be at high tide. When the tide recedes to its greatest extent, it is low tide. Tides can occur in several freshwater rivers and lakes, as well as seas and oceans. High and low tides are caused by the moon’s gravitational pull on the Earth and the Earth’s rotational force. The side of the Earth nearest to the Moon will experience the strongest pull, causing oceans to rise and high tides to occur. The rotating force of the Earth is greater than the gravitational force of the Moon on the side facing away from it. Because the rotational force causes water to build up as it tries to resist the force, high tides arise on this side as well. The ocean recedes elsewhere on Earth, resulting in low tides. The Sun’s gravitational attraction also plays a minor influence in the production of tides. Tides circulate the Earth as bulges in the ocean.
Types of Tides:
Semidiurnal and mixed semidiurnal tides are the most common type. It consists of 2 high tides and 2 low tides in one lunar day (approximately 25 hours). The difference in height between the high tide and the low tide is called the tidal range. In Hawaii, we experience these types of tides.
Diurnal tides consist of just 1 high tide and 1 low tide on each lunar day.
Hawaiian Tides: a lack of tidal variation
The Hawaiian islands tend to experience more mixed semidiurnal tides due to their geological origin. There are less tide swings due to the fact that they tend to lack large bays (>15 square miles in size). Large bays and coves can “funnel” water near the shore and amplify wave action. These large bays are a common sight in places such as Northern Australia and Europe. In addition, the absence of a continental shelf inhibits tidal variation. The archipelago was formed due to an underwater hotspot in the middle of the Pacific Ocean. This hotspot allowed magma to push through the Pacific Plate and form volcanic eruptions. Over many millions of years of eruptions, a chain of islands were formed. However, due to the volcanic origin of these islands, Hawaii does not contain places with a deep continental shelf. These underwater features heighten the process of wave shoaling. This phenomenon allows waves to appear “steeper” in appearance, increasing in amplitude and decreasing in wavelength. As a result, tides along coastlines with continental shelves increase in magnitude.
Types of Weathering:
Physical weathering, also known as mechanical weathering, is the process class that causes rocks to disintegrate without chemical change. Abrasion (the process by which particles are reduced in size) is the primary process in physical weathering. Due to temperature, pressure, wind, water, etc. physical weathering may occur.
Chemical weathering changes rock composition, often transforming them into different chemical reactions when a solute interacts with minerals. Chemical weathering is a gradual and ongoing process as the rock mineralogy adjusts to the environment near the surface. Chemical weathering best occurs at higher temperatures and humid climates.
Biological weathering is the weakening and subsequent breakdown by plants, animals and microbes of rock. For example, growing roots of plants can put stress or pressure on rock. Even though the process is physical, a biological process exerts the pressure. Biological processes can also produce chemical weathering, such as when organic acids are produced by plant roots or microorganisms that help dissolve minerals.
Logging Tasks:
- Using your observations at the viewpoint and the site https://tidesandcurrents.noaa.gov/noaatidepredictions.html?id=1617846 for tide predictions for Kailua-Kona, was your visit near low tide or high tide?
- How did the tides affect the appearance of the mini tide pool during your visit? Was the tide pool empty, covered completely, or partially covered in seawater?
- Were there any shell pieces, sand, pebbles, or other debris found in the tide pool? Describe what you see during your visit.
- What type of weathering mentioned in the description seems to be affecting the rocks at the GZ?
- As of June 2019, earthcaches now contain required photo logging tasks. Please provide a photo of yourself, your GPSr, or a personal item that proves that you have visited this site. You can put this in your log.
Sources:
https://www.thoughtco.com/tidal-pool-overview-2291685
https://www.americanoceans.org/facts/information-guide-high-low-tide/
http://www.hurricanescience.org/science/basic/tides/
https://stabmag.com/news/why-are-tides-so-tiny-in-hawaii-and-enormous-in-europe/
https://www.geologypage.com/2016/05/weathering.html
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