The rest area is on the East Bound I 90. If you are heading west you must cross over I 90 at the next exchange.
Looking south from the rest area is Sprague Lake which is a 1.25 by 5 mile deep lake. At first glance you might say it is just another lake and you will be right, it is just another lake. What makes it special is how it was formed. It may help to have maps of Washington, Idaho and Montana (use Google Earth) to help visualize the scope of happenings that cause this lake to form.
To log this cache answer the following questions and e-mail me your answers.
For subject put down Sprague Lake EC.
List those people who will get credit (if there is more than one cacher).
At GZ look at the area south of the lake and beyond the resort (one mile plus) and describe what the land looks like.
Now go to the east end of the rest area and look down at the gully and describe what you see.
Do you think what you see looking in the gully will be about the same as what you would see south of the lake in the distance?
Feel free to post pictures but do not post any pictures about the questions.
Bonus question on trains. What is a cow catcher and where would you find one on a train? If you don’t know make up something humorous and put it in your log.
SP R A G U E L A K E W A S F O R M E D B Y F I R E, I C E, A N D F L O O D S
T H E F I R E
For more than 10 million years (6 to 16 million years ago) one lava flow after another covered this land and is known as the Columbia River Basalt group. There were 175 known flows in Washington state alone and with flows from eastern Idaho (Craters of the Moon), to northern California and far out in the Pacific. The weight of the lava caused the earth’s crust to sag The lava flowed out of vents 30 feet wide to 300 feet long called feeder dikes. Individual flows were 50 to 300 feet deep and some area erupted up to 7 times. The thickest lava is around the tri-cities south of Sprague Lake and it has been measured to almost 3 miles deep. As you cross the Columbia Bridge on I-90 look at all of the basalt cliffs above and below the bridge. The lava must have been very liquid and formed lots of lava tubes. Each eruption has unique properties that can be used to identify separate eruptions. Some eruptions started at the far northern limits and ran to the far southern limits of the Columbia River Basalt groups.
As the hot molten lavas started to cool cracks formed in the basalt. Some of the thicker basalt layers may have taken 50 years to cool. Remember-heat expands and cold contracts and that is what happened to the magma. Some of the lava shrank and formed basalt columns. Most are 4 and 5 sided and can be 50 plus feet tall. It now has been 6 million years since the last eruption and normal freeze and thaw and erosion cycles and a few Teutonic fractures (earthquakes) further widen the cracks, which will play an important part in forming Sprague Lake.
T H E I C E
No one knows exactly when the last ice age started but 40,000 years ago is a good guess and its peak was about 15,000 years ago. This glacial sheet covered Idaho to Sandpoint and the north Columbia River almost to highway 2 in Washington and in Montana to almost Missoula. We know that it was 2,500 feet above ground at Sandpoint which would have made it 4,500 feet above sea level. Geologists use this elevation as a rule of thumb in Washington. Only the tops of the mountains were showing and the Valleys were total ice moving south.
Glaciers are form when more snow and ice are accumulated in the cold seasons than the ice melt in warmer seasons. As long as this happens the glaciers keep growing. When it is reversed the glaciers shrink (most of the US glaciers are gone or soon will be unless the warm weather cycle reverses). These glaciers had 25,000 years to grow and produced an ice dam 2,500 feet high and covered Sandpoint Idaho and Pend Oreille Lake. This ice flow came from Canada and flowed south down the Purcell trench. The Clark Fork River starts east of Missoula, Montana and runs over 170 miles to Sandpoint, Idaho. As the ice dam backed up the Clark Fork River at Sandpoint. Lake Missoula was formed. It was 2,000 feet deep at the ice dam and 950 feet in the Missoula valley. The volume of water would be more than Lake Ontario.
F L O O D
No one really knows how the dam broke but several theories are likely. The first is the lake got so deep it floated the dam like a big ice cube. The second is that the ice is always moving and it forms cracks and as the water behind the dam found the cracks it enlarged them until the whole dam was rotten with cracks and broke. Regardless what broke the dam huge icebergs containing boulders captured by the glacier flowed south picking up debris and scoured everything it touched.
First that went was vegetation, if the trees were not broken from the debris they were knocked over as the flood eroded all top soil down to bed rock. When it got to Spokane (about 70 miles below the dam) it was going 80 MPH and over 700 feet high. Some water turned west and followed the leading edge of the glacier until higher ground pushed it south and carved out the walls where the I 90 bridge is. Some went southwest to where you now stand and joined the Columbia River at the tri-city area. This scouring action attacked the cracks in the basalt and broke it from the lava beds and added more debris to the flood. This scouring action created the valleys (coolies) that are basalt lined. The flood only lasted 2 or 3 days but its’ destruction made the land to look more like the moon than earth. Geologist can identify at least 33 separate floods but suspect it could be more. Each flood did more and more damage to the land until the floods ceased.
Imagine standing here when the biggest flood came. You would have heard the loudest noise ever with the shaking of the ground as the big icebergs, boulders and trees tumbled. A wind would be created as the wall of water miles wide and hundreds of feet high pushed the air aside. Looking left minutes after hearing and feeling the flood coming you would have seen the wall bearing down upon you gouging the earth as it went by exiting to your right. The smaller floods later on would keep shaping the lake until the last flood being weaker would have deposited small debris that created the natural dam on your right. All of this area that the flood created is called the “Scab Lands. If you look at google earth and zoom to see the central part of Washington you can tell where the flood travelled by how barren it still is. Sprague Lake is unique as it runs east to west rather north to south as most of the lakes do in this flood area. The hill behind you may have had an influence on the direction of the lake. Oh yes, it is a great lake to fish for many varieties, but it is known for being windy.
References Glacial Lake Missoula David Alt ICE Age Flood Bruce Burners, Eugene Kiver ake Missoula