FIELD MAPPING

Summary

Mary Seed, a bedrock geologist with the Illinois State Geological Survey, explains the process of creating detailed geological maps. She demonstrates how she uses tools like a compass, field book, and Brunton compass to gather accurate data in the field, from measuring rock formations and jointing to determining elevation. Mary also discusses the challenges of mapping in areas with limited outcrops and how she deals with hazards like steep bluffs, ticks, and poison ivy. The video highlights the importance of understanding map scale and the role of winter mapping in overcoming environmental obstacles.

Takeaways

• 😀 A field geologist uses a waterproof field book and compass to gather data in wet conditions.
• 😀 Correct location identification is crucial for accurate geological mapping and note-taking.
• 😀 The compass helps determine the direction of features, such as streams, to orient maps.
• 😀 Geological notes include weather conditions, rock characteristics, and sedimentary structures.
• 😀 Geologists use rock hammers to examine fresh rock surfaces and note characteristics like grain size and bedding.
• 😀 Jointing in rocks is another important feature geologists measure using a specialized Brunton compass.
• 😀 Geologists may need to rappel down bluffs to accurately measure rock outcrop heights.
• 😀 In cases where outcrops are sparse, drilling is used to gain insights into underground stratigraphy.
• 😀 Topographic maps are essential for identifying features but may lack details like small ravines.
• 😀 Hazards in the field include poison ivy, steep bluffs, snakes, and ticks, with some mitigated by winter mapping.
• 😀 Fieldwork is more efficient in the winter, with geologists covering more ground compared to the summer heat.

Q & A

What is the primary task of a bedrock geologist like Mary Seed?

Mary Seed, as a bedrock geologist, primarily focuses on making maps and studying the geological formations in the field. She uses tools like a compass, field book, and rock hammer to collect data on rock types, bedding, jointing, and stratigraphy, which helps in creating accurate geological maps.

Why is it important for a geologist to know their exact location in the field?

Knowing the exact location is crucial for a geologist because it ensures that the notes and data collected can be accurately referenced and replicated later. Without correct location data, observations may become useless, as they cannot be placed back in the correct context.

How does Mary Seed determine her location in the field?

Mary Seed uses a compass in conjunction with a map to determine her location. By measuring the cardinal direction of a feature, such as a stream, she can align her map with the compass and pinpoint her position.

What is the purpose of using a field book during geological mapping?

The field book is used to record all observations and data collected during fieldwork. It helps document details such as the type of rock, weather conditions, and geological features. The waterproof nature of the field book ensures that notes remain legible even in adverse weather conditions.

What is jointing in geology, and why is it important to note it?

Jointing refers to the natural fractures or cracks in rock formations. These joints can be critical for understanding the structural integrity of rock, the movement of groundwater, and potential hazards in the area. Geologists measure the direction and angle of these joints to gain insights into the rock's formation.

How does a Brunton compass help geologists in the field?

A Brunton compass is a specialized tool used to measure the orientation of rocks, including their dip and direction. It allows geologists to accurately measure angles and the alignment of geological features, providing crucial information for mapping and analysis.

What challenges do geologists face when measuring outcrops in areas with steep bluffs?

Measuring outcrops in areas with steep bluffs presents challenges such as limited visibility and difficulty in accurately measuring heights. To overcome this, geologists may use a rope and staff to repel down the bluff and measure the outcrop by counting eye heights from a fixed point.

Why is topographic mapping important in geological surveys?

Topographic mapping is essential for understanding the terrain and layout of an area. It helps geologists identify features such as ravines, slopes, and outcrops, which are crucial for mapping the distribution of rock formations and understanding the area's geological history.

How does soil cover and vegetation impact geological mapping in areas like Illinois?

In areas with significant soil cover and vegetation, bedrock can be obscured, making it difficult for geologists to directly observe rock outcrops. This necessitates using alternative techniques, such as drilling to gather information about the underlying geology and connecting data from known outcrops.

What are some of the hazards geologists face while mapping in the field?

Geologists face various hazards while mapping, including poison ivy, snakes, steep bluffs, slippery rocks, ticks, and chiggers. These dangers can be mitigated by choosing the right time of year for fieldwork, such as winter, when conditions are cooler and less hazardous.