South Michigan EarthCaches 


Blue Ridge Gravel Pit EarthCache Part 1 – Glacial Esker 

Connection to the Earth Science Curriculum

Essential Lessons:

The Blue Ridge Gravel Pit provides an opportunity for visitors to discover two interesting stories that involve orange-brown boulders or fragments of sandstone found that tell of times when the climatic conditions were vastly different in Michigan than they are today.

Earth Science Literacy Principles

  • Big Idea 2.1. Earth's rocks and other materials provide a record of its history.
  • Big Idea 2.7. Over Earth's vast history, both gradual and catastrophic processes have produced enormous changes.
  • Big Idea 3. Earth is a complex system of interacting rock, water, air, and life.
  • Big Idea 5. Earth is the water planet.
  • Big Idea 7. Humans depend on Earth for resources.

Common misconceptions

  • Glaciers are ice and snow deposits on the land were no more than 50 feet thick.
  • Glaciers most recently covered Michigan millions of years ago.
Key Earth Science/Geological Vocabulary Words:

Cementation: The process of binding sediments or grains together to make sedimentary rocks.

Esker: A long winding ridge of gravel, sand, etc., originally deposited by a meltwater stream running under a glacier.

Glacial Till: Unconsolidated, heterogeneous mixture of clay, sand, pebbles, cobbles, and boulders deposited onto the landscape by retreating glaciers.

Laurentide Ice Sheet: A massive sheet of ice sheet that covered most of Canada and a large portion of the northern United States between 95,000 and 20,000 years ago.

Pleistocene Epoch: A small unit of time within the Cenozoic Era that encompasses the most recent glacial advances on our planet between 11,700 and 2.58 million years ago.

Wisconsinan Advance: The most recent period of continental glaciation in the northern hemisphere that occurred between 10,000 to 70,000 years ago. The height of the Wisconsinan Advance occurred nearly 20,000 years ago when glaciers made their furthest advance toward the equator.

Developed by: Mark Reed

The Blue Ridge Gravel Pit is owned by the Jackson Country Road Commission and provides an opportunity for approved visitors (Permission must be obtained, see access information below) to discover two interesting stories that can be told that involve orange-brown sandstone boulders or fragments found within it. These boulders tell a story of when climatic conditions were vastly different than what they are today in Michigan.

Coordinate: N 42° 09.573′ W84° 21.231′

Materials needed for visit:

Permission from the Jackson County Road Commission, the information provided, GPS, magnifying lens, rock hammer, safety goggles, and a sketchpad or camera.

Description:

The Blue Ridge Gravel Pit owned by the Jackson County Road Commission, is located east of US 127 about 6.5 miles south southeast of Jackson, Michigan. It is an interesting site in many respects due to the fact that the mining of sand and gravel has exposed the interior of a glacial esker. The esker measures over 5 miles in length and its sediments are likely from a variety of locations from within both Michigan and Canada. The Blue Ridge Gravel Pit provides a window into the past that tells of a time over 10,000 years ago when a flowing "river" within the ice was able to move both melt-water and sediments onto the landscape in front of a retreating glacier.

An esker is a "stream-tunnel" within a mass of ice that deposits a tubular structure onto the landscape as a glacier retreats (Figures 1 and 2).

Figure 1: Landforms Associated with the Retreat of a Continental Glacier. Please Note the Corresponding Relationship between the Formation of an Esker and a Stream Tunnel.


Figure 2: Exposed Sub-glacial Melt-water Tunnel Deposits are called Eskers.


As a continental glacier retreats, sediments consisting of rock, gravel, sand, and silt are deposited as "outwash plain" in front of the glacier (Figure 3). The size and types of sediment that can be carried by a melt-water stream is largely determined by its velocity and volume.

Figure 3: Outwash Plain and Continental Glacier


Streams or melt-water sources carry sediments in three different ways. Dissolved and suspended material is carried downstream within the water column whereas the heavier particles are able to skip or roll along the bottom of a flowing body of water. In other words, large boulders and stones require greater energies to be able to move them when compared to small sediment such as silt or sand.

Today, perched or winding ridges (Figure 4.) that appear of a glacial origin are called eskers and are considered to be valuable resources to a region. These rich deposits of sand, gravel, and rock are often mined by businesses or governmental agencies because they support a variety of construction needs including the creation and maintenance of roads and highways.

Figure 4: Perched Ridges of Sand, Gravel, and Rock are called Eskers.


The Blue Ridge Esker of Jackson County is often recognized nationally by Geology students and professors as a classic esker and glacial outwash plain. Maps such as the topographic map shown in Figure 5 have been used to teach Geology students how to recognize different landforms and their origins associated with continental glaciations. The Blue Ridge Esker appears on the map as a narrow brown feature with contour lines that are in close proximity to each other. Swampy areas on the map provide clues in regard to glacial outwash and blocks of ice that had once broke off the body of the main glacier have created numerous kettle lakes and ponds in the area.

Figure 5: Blue Ridge Esker – Jackson County, Michigan. USGS Topographic Map


N 42° 09.619′ W84° 21.307′

Figure 6: The North-Northeast Cut of the Blue Ridge Gravel Pit - July 2011.
Photograph by Mark S. Reed


Visitors may observe within the Blue Ridge Gravel Pit (Figure 6) how sediments have been sorted, weathered, and deposited as they were carried by the glacial melt-water flowing under the ice as a river. From the floor of the gravel pit, the banks cut into the esker rises nearly 70 feet in places. Evidence of both stratification and cementation are easily observed at this location. To people mining the gravel pit, cemented material is known as a "clinker" as shown in Figure 7.

Figure 7: "Clinker" or Cemented Rocks and Sediment.
Photograph by Mark S. Reed


However to Geologists, this "clinker" material that is held together by dissolved mineral "glue" has created a temporary but unique structure that illustrates several concepts from the Rock Cycle that relate to sedimentary processes. These concepts relate specifically to the sediment origin, their transport, sorting history, deposition, and cementation.

Question 1:

This structure should be observed from at least 15 feet away since it has the very real potential to collapse as the cemented particles are weakened by the elements, vibration, and human activity.

Sketch or photograph this structure and describe the types and sizes of the sediments within it. What classes (Igneous, Metamorphic, and Sedimentary) or types of rocks (Sandstone, Granite, Limestone, Schist, etc) are present? How what specific ways do the types, sizes, and appearance of the various types of sediments relate to the Rock Cycle?

Access Information:

Safety and Courtesy Note:

Since the Blue Ridge Gravel Pit is owned by the Jackson Country Road Commission, permission must be first obtained to enter. Visitors need to be vigilant in regard to safety and not attempt to climb steep slopes, get too close to cemented overhangs and structures, or climb up sand piles or slopes that could potentially collapse.