The Birth of a Cave

Have you ever gone spelunking? Spelunking, also known as caving, is not well suited for everyone. It can be an extremely dangerous pastime for the ill prepared and foolhardy, but it can also be a fun and exciting adventure for those who know what they’re doing. Newton cave can be found on cave ridge along with 13 other limestone caves (Haliday 1963). These are some of the few limestone caves in Washington which has made them popular with most spelunkers in the state. People that enjoy caving often join the National Speleological Society and form up into local groups called Grottos which is the Seattle area is known as the Cascade Grotto. In addition to the addictive fun of caving, this outdoors experience includes a hike (more of a climb really) and a beautiful campsite that looks out over the Cascade Mountains.

The story of Newton Cave began many millions of years ago and thousands of miles to the south of Washington State in the Pacific Ocean as microscopic sea shells collected in a shallow coastal margin, forming a sedimentary rock called limestone. This limestone experienced great temperature and pressure turning into a metamorphic rock called marble which is the same stone Michelangelo used to carve the statue of David. This area of marble became part of a slowly moving plate of rock that moved northward eventually running into the North American plate. Similar to how the impact of the Indian Plate on Asia raised up the Himalayan Mountains, the impact of the Pacific plate gave rise to the Cascade Mountains. Most of the Cascades formed as a result of the subduction of the heavier oceanic plate beneath the continental plate which melted and gave rise to Mount Rainier and the other volcanoes.

According to the USGS geological surveys of the Snoqualmie Pass quadrangle, the marble in which Newton cave formed is between 30 and 60 million years old (Tabor, Frizzell, Booth, and Waitt, 2000). In this case, marble was scraped off the subducting oceanic plate and pushed onto the North American plate through a series of low angle thrust faults, creating a formation known as an accretionary wedge. The area of former oceanic floor came to rest at the top of the Cascade Mountains at the same elevation as the top of the Alpental ski area. It is located just across the valley east of the ski area on a high mountain ridge line between Mount Snoqualmie and Guye Peak. Imagine climbing on rocks at the very top of the North Cascades and finding fossilized remains of ancient sea shells. Even more amazing, the marble area, commonly referred to as cave ridge is now riddled with caves and sinkholes forming a terrain geologists refer to as karst topography (Alpha, Galloway, and Tinsley, 2004).
Newton cave is the largest cave located on cave ridge. The cave formed in the marble as an erosional process. As rain water moves through decaying vegetation it can pick up small amounts of carbon and become a very dilute carbonic acid. Marble and limestone are both formed from calcium carbonate which the same mineral that forms sea shells. Calcium carbonate rocks can be dissolved by acids (Mogk, 1978) resulting in the formation of caves. As the water becomes saturated with calcium carbonate and then evaporates within the cave, it leaves deposits of calcium carbonate that form the speleothems we commonly associate with caves such as stalactites, stalagmites, flowstone, the (Haliday, 1963) shapes of the rooms and caverns, and many other features commonly found in caves.