Greater Seattle Area - Climate, Weathering and Mass Wasting

The climate of a particular area is dependent upon where it is located. As you can see, the United States has many climate zones. In South Florida, we are located in the Tropical Wet/Dry Season climate zone. Well, if you live in Florida, then you already know how the weather is and don't require an explanation. Besides, I am not going to focus on South Florida at this moment. I am focusing on the Greater Seattle Area (GSA).

This map can be found on the following page: Summary of the Museum Preservation Environment Summit

In the Greater Seattle Area (GSA), we tend to find the climate is a combination of Marine and Highland  (alpine). What does that mean though?

Marine

A marine climate consists of humid weather with lots of rain and is never too hot or cold. It is also cloudy for much of the year. 

As you can see from the picture below, taken in September 2012, the cloud coverage can be very dense. It sits on top of the area like a blanket. I took this picture as we were driving, so it isn't the best, but you get the point.

This next picture (again, while we were driving), shows the area about to receive a nice amount of rain. This type of rainfall is not typical. Usually, when it rains, it is a very light, misty sort of rain. The misty rain can last all day. These heavier rainstorms do occur, but not as frequently as the lighter rainfall.

Highland

Highland is exactly what the name suggests. It is an area found in mountains and/or high plateaus. Summers range from June to September. The temperatures go from cool to cold. The higher you ascent, the colder it becomes. The summers are mild, while the winters are quite cold. Most of the precipitation is in the form of snow.

As you can see from the pictures below, taken in March 2013, there is a LOT of snow! The pictures below were taken while we hiked along a HUGE embankment of snow in the Paradise section of Mount Rainier. It must have been at least 10' high.  However, I digress, it was just as beautiful as it is in September! 

The Pacific Ocean has a lot of influence over Mount Rainier, the west coast of the Cascades and also over Olympic National Park. Maritime air masses bring the mild weather, humidity and rain. However, if the Olympic Mountains block the polar masses coming off of the Pacific Ocean, then why isn't the weather in the GSA (Greater Seattle Area) more arid, like the east side of the Rocky Mountains? The reason for this is something known as the Puget Sound Convergence Zone.

Basically, the polar air masses coming off of the Pacific Ocean are split, one follows along the south side of the Olympic Mountains, while the other runs along the Strait of Juan de Fuca. They continue east until they hit the Cascades. The one coming from the north, heads south. The mass from the south heads north and then they both collide or converge. Since there is nowhere else for them to go, they push back up into the atmosphere.

They settle approximately over the Snohomish county area, which is located between the Cascades and Seattle. I always wondered why at Snoqualmie Falls it would be snowing, but when we made the drive back to Bellevue, as soon as we passed over a certain point - it just disappeared. Of course, since I am from Florida, seeing snow any chance I can get is certainly a treat.

As I began to do my research for this portion of the blog post, I began to understand.  Also, the convergence zone can actually be pushed further west or fall further east, depending upon the strength of the wind. You can read more about this phenomenon in this informative article: "What is the Puget Sound Convergence Zone?"     

Weathering

Weathering is a process by which rocks are chemically altered or physically broken down as a result of atmospheric agents and the pressures/temperatures at or near the Earth's surface.

Some of the physical weathering processes in the GSA are frost action (at higher altitudes in the Cascades, Olympic Mountains and Mount Rainier), talus and abrasion (wind, rivers, waterfalls and glaciers). Some examples of biological weathering are root wedging and lichens.

Below are some pictures of Snoqualmie Falls taken September 2012. Take note of the weathering as a result of the rushing water (also a form of water erosion) of the waterfall:

   

Rock fragments are a product of the weathering process in these areas as well. Notice the boulders in the picture below (Deception Pass - March 2013). Over time, those huge boulders break down into smaller rocks, cobbles and pebbles like the ones in the next picture on the beach. The waves toss and smooth the rough edges of the rocks. See how some pebbles have a rounder shape than other pebbles? This is known as spheroidal weathering.

Spheroidal weathering also occurs on the banks of rivers and streams. (Mount Rainier - 2013)

Mass wasting:

Mass wasting is the down slope movement of earthen materials under the force of gravity. There are many types such as soil creep, rockslides, rock falls, landslides and mudflows. Considering the GSA has many volcanoes and mountains in the region, it is only logical to assume that many of these occur in the region.

The current peak of Mount Rainier was formed by an event known as the Osceola Mudflow about 5,600 years ago. The east and northeast slopes collapsed and flowed down as far as Puget Sound. Then subsequent mudflows and lahars followed. Much of the Cascades are subject to mudflows or landslides especially because the area receives a high amount of precipitation. 

You can read more about these events here: 

Significant Lahars at Mount Rainier 

The picture below and more information can be found here: 

Huge rockslides at Mount Rainier

It's extremely frightening to think that there is a possibility you may get caught in one of these mass movements of earth. However, I enjoy the area and will continue to take that chance every time I visit. Anyway, you take a chance every single day, even just by taking a shower, walking out the door or getting behind the wheel of a car. I want to live life to the fullest and not worry about something that *might* take my life. The area is too majestic to avoid. :-)

Thanks for reading!

~ Crystal ~