WELCOME TO MASTODON ISLAND PENINSULA!
Background Info
If you’re standing at the posted coordinates, you are standing in between what was once, in fact, two separate man-made islands. The area in which Mastodon Island peninsula is located was once a boggy marshland. In 1934, The Civil Works Administration was contracted to dig out the marshland to create a municipal lake, which was to be called Townsend Lake. The North island was created first through deposits from the excavation and the South island was created later, in the same manner. It is unknown exactly when the two islands were connected to create the single island, known today as Mastodon Island. Soon after lake excavation began, several Mastodon bones were unearthed along the Eastern shore of the lake. (In fact, it is rumored that a full Mastodon may still be buried along the Eastern edge of the lake, near “the big rock” near N41 44.281 W088 17.794) The public enthusiasm with the Mastodon bones led to the lake being officially named “Mastodon Lake.”
Layers of Earth at Mastodon Island
In 1990, scientists studied six layers of earth at Mastodon Island. The earliest samples (#1 "Diamicton") dated back to more than 14,000 years old. From the base level to the top surface on which you’re standing (#6 "Fill") , the layers in order are as follows:
#1 Diamicton, matrix-supported, with a silty clay matrix, or very poorly sorted sand and gravel outwash about 15m thick
#2 Organic-rich silt, uniform to laminated, about 0.5m thick
#3 Gyttja, a dark green-colored coprogeneous lake sediment, about 5m thick
#4 Marl, an unconsolidated sedimentary rock or soil consisting of clay and lime, about 3.1m thick
#5 Fibric peat with matted vegetation, about 1.7m thick
#6 Fill, comprised of redepositied clay, marl, diamicton, bricks, mortar, sinter, ash, glass, and other debris, about 2.3m thick.
Today, you are standing on the top layer, which is the “Fill” described in #6. The Mastodon bones were discovered in the marl, described in #4.
Shoreline Erosion
Over the past 85+ years, the shorelines of Mastodon Island (comprised of the #6 "Fill”) have eroded through various means. There are 3 main types of soil erosion:
1) Wind erosion – the removal of soil particles by the force and kinetic energy of wind.
2) Water erosion – caused by the kinetic energy of rain falling on the soil surface, by the mechanical forces of water runoff, or by ripples of lake water repetitively crashing into the shoreline.
3) Gravity erosion – mass movement of soil occurs on steep slopes under the influence of gravity. The process involves the transfer of slope-forming materials from higher to lower grounds due to self weight.
Shoreline Restoration
If you stood at the posted coordinates several years ago, you would have noticed the erosion along the island’s shoreline. Today, there is not much evidence of erosion. This is thanks to the restoration efforts that took place in 2018-2019.
There are 2 main types of shoreline restoration: soft-armored bioengineering and hard-armored bioengineering. They can be utilized separately or in conjunction with each other.
1) Soft-armored bioengineering – includes planting vegetation along the shoreline, laying down biodegradable netting on the banks, placing large natural logs or woody debris along the banks, re-sloping the shoreline banks to create a gentler slope for runoff water.
2) Hard-armored bioengineering – includes distributing large rocks along the shoreline, seawalls, installing concrete or wooden bulkheads, and installing drainage systems.
Logging this Earthcache
In order to log this Earthcache, send me a message with the answers to ALL 3 of the following questions:
PLEASE DO NOT POST ANSWERS IN YOUR LOG.
PLEASE SEND THE ANSWERS IN A SEPARATE MESSAGE PRIOR TO LOGGING THIS EARTHCACHE! DISCLAIMER: LOGGING THIS EARTHCACHE WITHOUT SENDING ME THE ANSWERS AHEAD OF TIME (OR WITHIN 7 DAYS OF LOGGING) MAY RESULT IN YOUR LOG BEING DELETED!
1) Standing at the posted coordinates, describe which bio-engineering techniques you see utilized along the shoreline around the lake. Do you see vegetation, netting, woody debris, soft slopes, large rocks, seawalls, concrete or wooden bulkheads, drainage systems? There may be more than one technique in place. (Hint: one technique is being utilitized across the lake to your East.)
2) Which of the 3 types of erosion listed above do you feel was most responsible for the shoreline erosion at Mastodon Lake? Why?
3) Fill in the blank: In a further effort to preserve the surrounding natural landscape, the Mastodon Island shoreline has been improved and _____________ to reduce erosion and improve the natural habitat." This answer can be found on the blue educational sign located near N41 44.285 W088 17.836.
I will actively monitor logs and answers sent. Photos may be deleted at CO's discretion if they provide clues/answers to question #1.