July 1, 2021
Are Michigan’s landforms at risk of erosion?
“Ask the Expert" articles at Michigan State University provide information and insights from MSU scientists, researchers and scholars about national and global issues, complex research and general-interest subjects based on their areas of academic expertise and study.
In May, the arch in Darwin’s Arch in the Galapagos Islands crumbled into the sea due to natural erosion. Recently, a 200-foot piece of Pictured Rocks fractured and slid into Lake Superior. Causing Michiganders to wonder if 2020’s record high water levels in the Great Lakes, could increase coastal erosion on Michigan’s beloved landforms and lakeshore homes?
Danita Brandt, associate professor in the Department of Earth and Environmental Sciences within the College of Natural Science at Michigan State University, explains how erosion is a natural process that inevitably alters landscapes over geological timescales.
Phanikumar Mantha, professor in the Department of Civil and Environmental Engineering within the College of Engineering at MSU, explains what we can do to mitigate the effects of coastal erosion on human timescales.
1. What is coastal erosion?
Brandt: Coastal erosion is the result of the interaction of waves, currents, wind, ice and gravity with a shoreline. It is a naturally occurring part of Earth’s surface processes that include weathering, erosion, transport and deposition of sediments and rocks.
Mantha: Coastal erosion collectively refers to the processes of breaking down, picking up and carrying away material (e.g., rock or sand particles) along our coasts by moving water and/or wind. When water slows down, the particles are dropped, and the process is called deposition. Erosion and deposition are two sides of the same coin and these are the same natural processes that shaped our shorelines in the past and continue to shape them today.
2. How is coastal erosion affected by the Great Lakes?
Brandt: The impact of coastal erosion in Michigan is directly related to lake levels; higher lake levels mean more erosion. Last year’s record high lake levels affected all Michigan residents, directly or indirectly, as not only private homes but facilities in our shoreline state parks were damaged or destroyed. Lake levels are down this spring, just in time to help rejuvenate the economies of local lakeside communities by exposing more beach. We are a state of two peninsulas. We will always have coastal erosion with which to contend. “How big a problem” coastal erosion is in Michigan is will be determined by how we think about this natural process — as a “problem” to be solved (temporarily) through engineering solutions or as a fact of living on a dynamic planet and the complexities that entails.
Mantha: Water currents in the Great Lakes are mainly driven by winds. When wave and current patterns change locally (due to natural processes or human activities), they can trigger changes in erosion/deposition patterns. We are experiencing a higher frequency of extreme wind speeds and larger waves as lake surface temperatures are on the rise and these translate to higher erosion potential. In addition, higher lake levels and shrinking ice cover on the lakes lead to more erosion. Winter ice cover can shield water from the effects of surface winds while protecting shorelines from severe winter waves. However, decreasing ice cover on the Great Lakes means that erosion and shoreline impacts continue to occur during the winter months as well.
3. How does coastal erosion threaten Michigan's landforms — such as beaches, sand dunes or large rock formations — and lakeshore homes?
Brandt: Erosion is a natural process. It becomes a threat or a problem when humans — our lives, possessions or livelihood are affected. “Natural processes” — volcanism, earthquakes, floods, erosion (mass wasting) — become “natural disasters” when humans are affected. The Earth is a dynamic system. Natural features and human structures, like houses, are ephemeral, geologically speaking; they may be long-lived on a human timescale, but Earth is constantly changing, responding to both internal forces that build mountains and cause earthquakes and give birth to volcanoes, and external processes that are powered by Earth’s atmosphere and hydrosphere.
To frame the discussion of the erosion and eventual collapse of these structures as a “threat” does not acknowledge the inevitability of the natural outcome and often leads to expensive and ultimately futile efforts to deny the reality of Earth’s constant change and the need to work within that reality.
Mantha: Erosion and deposition are natural processes that will always be there. Our coastlines are constantly changing in response to changes in the fluxes of sediment delivered to the nearshore regions by rivers, lake currents and wave action. This means that if we examine the sediment budget — the amount of sediment coming in and going out of an area of interest — we find that some areas along the coastline are losing sediment while other areas are gaining. The rates of these natural processes are accelerated as the intensity and frequency of extreme storms increase with undesirable consequences (e.g., beachfront homes toppling into the lake following bluff erosion, lost beaches, lost sand dunes, etc.).
4. Is there anything humans can do to stop or at least slow down coastal erosion?
Brandt: Yes. To the extent that we humans contribute to climate change, specifically, global warming, which causes higher sea-level and more frequent and stronger storms, we might slow coastal erosion by taking measures to reduce levels of carbon dioxide emissions in the atmosphere.
Mantha: Yes. In addition to taking measures to reduce levels of CO2 in the atmosphere, we can begin by (a) taking actions to protect our coastal wetlands which help prevent erosion (b) planning carefully when it comes to designing and building coastal structures as they often have unforeseen consequences and can exacerbate local vulnerabilities in a warming climate (c) paying attention to and rethinking upstream activities (e.g., irrigation systems) that can decrease the supply of sediment to the nearshore regions (d) eradicating invasive plant species and bringing back native plants and grasses to our coastal areas to stabilize soils and so on. In areas where erosion is a major issue, shoreline stabilization works for some of the time, but it may be a temporary solution. Waves have a big role to play in sediment transport (wave power is proportional to the square of significant wave height); therefore, approaches based on reducing the destructive power of waves as they approach the shoreline have been used in the past (e.g., underwater structures designed to dissipate wave energy). These solutions tend to be expensive, though.
5. If we cannot stop coastal erosion, what could Michigan look like in the future?
Brandt: We tend to think of mountains and continents as immutable, permanent monoliths having always been where we find them today and lasting forever, but Earth’s tectonic plates are moving at an average rate of 2 cm/year; the Earth 250 million years ago looked very different from today, and the Earth of 250 million years in the future will be very different from today.
Mantha: Processes driving sediment transport are complex and highly nonlinear — a direct consequence is that long-term predictions over large areas come with significant uncertainties. This should not prevent us from acting now to brace for future changes, though. Coastal communities in other parts of the world have shown remarkable resilience and adapted to change, and we can learn from these lessons. It also helps planning to separate climate-related changes from non-climate impacts. In the end, a combination of sound science, innovative engineering solutions, policy and investment in coastal research, education and outreach will help us move forward.
Story by Emilie Lorditch, courtesy of MSUToday.