This earthcache is located at the north end of Richland’s Badger Mountain Park. Park at the parking waypoint provided and take a short walk on a paved trail to a viewpoint overlooking Richland and the confluence of the Yakima and Columbia Rivers.
The basalt hilltop at the viewpoint is part of the Elephant Mountain Member of the Saddle Mountains Basalt Formation. The Elephant Mountain Member was deposited during the upper Miocene epoch about 10.8 million years ago.
At the earthcache coordinates just to the west of the viewpoint is a rock outcropping of vesicular basalt. A rock you've probably seen many times, vesicular basalt looks a lot like swiss cheese. This earthcache explains how it got that way.
The vesicles are the holes formed when lava containing gas bubbles solidifies. They may be rounded, irregular, or elongated. Highly vesicular basalt is called scoria (more rock than bubbles) or pumice (more bubbles than rock). Pumice is a solidified froth of volcanic glass and can have so many vesicles that many times it will float in water.
Scoria is common in the layered flood basalts of the Columbia Basin but pumice is rare in the basin because it is formed from the ejection of highly pressurized, super heated rock from volcanoes that forms the glass froth from sudden cooling and depressurization.
Elongated or stretched vesicles can indicate that the lava was still flowing after the vesicles formed. The direction of elongation shows which way the lava was moving.
Vesicles that later are filled with minerals are called amygdules. The minerals that fill the vesicles are dissolved and carried into the vesicles by ground water. Common mineral fillings are silica (quartz), calcite, and zeolites (a group of hydrous silicate minerals that most people are familiar with as the solid stuff used in water softener systems). If you want to visit a location with excellent examples of amygdules, check out the Panhandle Gap Amygdules earthcache (GC5BTRV) near Mt. Rainier.
Vesicular basalt layers form both at the top and the bottom of lava flows. The vesicles in bottom layers often form from the contact of the lava with moisture in the surface the lava is flowing over. The vesicles in the top layers form from the pressure relief and expansion of gas within the lava. The vesicular basalt seen in the outcrop at the earthcache coordinates is a top layer of a lava flow. (The basalt formed from the interior of the lava flow can be seen in a nearby quarry if you walk in the other direction on the paved path from the parking lot).
To get credit for this earthcache:
Send me an e-mail with the answers to the following questions. (NOTE: Do not post the answers in your log or it will be deleted.)
- What is the approximate diameter or width of the larger vesicles in the outcrop?
- What do you observe about the size of the vesicles as you look from the bottom to the top of the outcrop?
- Regarding the above question, what do you think is the reason for what you observe?
Pictures are always welcome, but please do not post any that could provide information for the answers.
In and around the cache location appears to be a favorite hangout for locals as there is a good bit of broken glass bottles in the area, so please watch the little ones!
Congratulations to kiekefretter for the FTF! 