LESTER RIVER EarthCache

An Ancient Shoreline & Glacial Power

A 30 mile drive along the rim of the hills overlooking Duluth begins here along the Lester River and Amity Creek. The parkway eventually reaches the shoreline of ancient Glacial Lake Duluth several hundred feet above the present level of Lake Superior.

The Lester River courses through lava formations of the Keweenawan age. The lava that formed is dark basalt that was extruded in several flows one billion years ago. A closer examination of the rocks will reveal “bubbles” that formed from gas as the lava crystallized. There are more bubbles formed at the source of the lava then near the end. In this case the basalt is denser as you get closer to Lake Superior.

Although the last glaciers in Minnesota melted about 10,000 years ago, these rocks hold evidence of their passing. Outcrops at the mouth of Lester River are smooth but covered with scratches. Heavy glaciers with rocks and other debris at their bases worked like sandpaper to smooth out the rocks here, while individual pieces of rock scratched the glacial striations and crescentic fractures that you see leaving behind evidence to the direction of the glacial flow.

As the Ice Age came to an end the lake drained to the level of Sault St. Marie, Michigan, causing the streams to increase their cutting power. This gave rise to the gorges and waterfalls. The creek beds are relatively recent in geologic age compared to the gabbro outcroppings to the west and north.

A representative model of glacial abrasion.

TO LOG THIS CACHE:
1) How many feet of water would you be under if Glacial Lake Duluth existed today?
2) What direction was the glacial flow according to the glacial striations on the dark basalt outcrops behind this sign?

E-mail me the answers HERE.

Links:
- Duluth Skyline Parkway
- The History of Skyline Parkway
- Lester River
- Lester River Surf Forecast