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Local Weather History: The Good Type of Pothole

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Local Weather History:  The Good Type of Pothole

Road potholes are a problem for drivers, but the potholes we are discussing actually are a good thing.

They tell us about the climate as the glaciers receded tens of thousands of years ago & are very important, diverse ecosystems.

They are unique, but very common around the West Lafayette area.  However, there is the lack of them in Lafayette.

So...........

The last glaciation ended in our area ended more than 11,000 years ago, but ice arriving in the area & its recedence pattern has left marks on the land.  The recedence pattern is also tied to the climate at the time.

Where glaciers stopped, receded, then pushed again, ridges called moraines developed, while melting produced massive outwash plains.  Rivers & streams of water within the ice sheet deposited eskers or gravelly sandy ridges or they deposited kames of conical hills of gravel & sand.  The very edge of the ice sheet produced a terminal moraine, while a perfectly balanced melting & forward surge produced flat or gently undulating till plain.

A pothole is a hole filled with water formed with ice sheet recedence.  Many have filled-in to a degree naturally (some with peat) to produce "pothole" wetlands that are extremely important to plants & wildlife.  Potholes not fed by a stream or spring are called kettle ponds or kettle wetlands (if they have vegetation throughout).  They may or may not be tied to the water table.  For example, the kettles at Celery Bog occasionally dry out in Summer or Fall, making them ephemeral kettle wetlands.

This is a map of the northwest part of the Greater Lafayette area.

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This is a map of the known kettles or potholes (blue).  Note the sheer number of them on the west side, but the lack of natural potholes & lakes on the south & east sides.  Indeed, there were formerly swale wetlands & ponds on the southside & southeast side & beyond towards Romney & Clark's Hill, but a lot of it is pure till plain.

I also overlaid the vegetation at the time of European settlement in the same area.  Some of the lakes, ponds & potholes acted as natural firebreaks apparently, some not.

Can you image the wildlife & plant diversity with these wetlands all mixed with barrens, prairies, marshes & woodlands?  Imagine trudging through the area from present-day Purdue Baseball field to Celery Bog to Arbor Chase to University Farm in the year 1800?  The potholes would be filled with wildlife & plant diversity.  Imagine the sounds in the spring & summer before any development.  It would be quite an earful & sight to behold!

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So, why do we have so, so many holes on the West side?  Why Mulvey Pond, Hadley Lake, Celery Bog, etc.?  There use to be a lot, lot more, but they have been lost to development.  In fact, multiple potholes were destroyed for the construction of US 231 between Lindberg Road & Cumberland Avenue (mitigation for the wetland destruction is the pond with the large soil pile of east of 231 nearby).  A small piece of one is found looking northwest from the 231/Cumberland intersection.  It is about 90% filled in, but still supports Black Willow & some marsh plants (& Green Ash trees killed by Emerald Ash Borer).  Prior to 231, this area was loaded with Spring Peeper & Western Chorus Frogs.  The low, bowl-shaped area between Blackbird Farms & south of the Purdue Baseball & Soccer stadium & southward was once connected to Celery Bog as a solid lake. 

So many have been filled by development & agriculture, but some still exist, for example, like west of Inari or behind Pizza Uncommon off Win Henschel.  Hadley Lake is a large one.  

This is a glacial pothole or kettle pond in Greenland: 

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The potholes were formed by ice chunks crumbling & breaking off & outwash filling in around it as the ice was melting.  Rapidly-melting ice with the sheet may also have a turbulent stream at or near the base of the ice, which scours out a hole.  An ice chunk or multiple massive boulder being dragged with the receding ice sheet may also dig out an elongated kettle.

A more massive, massive ice piece may be tied to the ice sheet & be dragged, digging out a lake, as well.  It may then have become severe from the ice sheet & the meltwater of the chunk & sheet may form the lake.

So, what can we gather about the climate at the time on the west side that led to this swiss cheese arrangement of natural wetlands & lakes?  

Well, we need lots of ice breaking off the ice sheet of varying sizes & some of it melting rapidly while being partially attached to the parent ice sheet to give us the elongated kettle lakes.

Outwash needs to fill in around the ice quickly.  So, melting would need to be going at a rapid rate.

Large boulder would need to be dragged by rather rapid ice recedence too!

So, we can gather that this particular portion of the ice sheet on the west side was crumbling more than that part of the east side.

It could have been that the ice was darker in color via encountering more crushed rock & sediment on the west side.  This could have led to less albedo & more absorption of sun light.  The ice also may have been thicker on the east side at the time, making ice fracturing & severing more challenging.

Kettle formation in progress.........Alaska....

Note the very dirty ice & the bright white ice well behind it.  That dirty ice melts faster than the white ice.

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McCormick Road south of Lindberg:

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One of the Celery Bog kettle wetlands:

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Kettle remnant between Whitehorse Christian Center & Sheraton off Cumberland Avenue:

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Former kettle wetland near The Ivy off Cumberland Avenue:

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Mulvey Pond kettle pond north-northwest of Montmorenci:

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