Violent-Rain-and-the-Substrate.html

Daniel Brouse asked:
As the sea levels rise, how far "inland" might we see salinization of fresh water? Is it possible saltwater could infiltrate the Great Lakes?

• Lake Superior has an elevation of 600 feet above (current) sea level and a depth of 1,332 feet.
• Lake Ontario is 243 feet above sea level with a depth of 802 feet.

Greg Laden (an archaeologist who has worked extensively in coastal zones) replied:
Would not reach the Great lakes, but with a little erosion, the Hudson, Lake Champlain, and the St. Lawrence could become contiguous, so New England becomes an Island.

Daniel Brouse:
I am particularly interested in the Kennebecasis River (a tributary of the Saint John River in southern New Brunswick, Canada.) Do you have any thoughts on this process, in particular, the changing topography caused by extreme rain events? You can kind-of imagine Eastern and Western North America as giant beaches with ever increasing atmospheric waves splashing down on us. The Gulf Coast will be hit from both sides. We to see increasing intensity and/or frequency in a wide variety of violent rain events including: downpours, flooding, hurricanes, cyclones, monsoons, coastal flooding, storm surges, lightning and wildfires, hail, extreme wind, and concurrent extremes. The reign of violent rain has already begun. More hillsides and shorelines are collapsing. Atmospheric rivers are dramatically increasing flash flooding in the Northeastern USA. Worldwide, stormwater systems are becoming overwhelmed. Ironically, the streets of Abu Dhabi and Dubai, UAE, flooded days before the COP28 Climate Conference. Nowhere is safe from violent rain, not even in the desert preparing for a UN meeting on the climate crisis. As a result of increasing violent rain, new drainage culverts are forming. Eventually, the culverts will transform into recurring streams, carving new canyons, creating new landscapes and islands. Increased wildfires and landslides will transform topography. At the same time as the violent rain makes its way to the sea, the sea is rising to meet the violent rain. What do you think will happen to the floodplains in North America?

Greg Laden:
I have many thoughts on this, and this has been part of my research and study for a very long time, having done coastal archaeology in North America, etc. The basic question is what is the substrate? Sea level rise of 1 meter in Maine means the sea goes up to the top line that is currently 1 meter above the sea (we are ignoring tides) and that's it for thousands of years. That is because Maine is made out of granite. Sea level rise of 1 meter along Cape Cod, which is glacial till, means that the sea will erode horizontally many many meters. In fact, Cape Cod is a dead-peninsula walking, even given pre-AGW sea level rise. It will all wash away eventually, except any rocky bits of bedrock that might be there (but they aren't there AFIK.) So, given that, yes, storms come in to play. The rate of erosion of Cap Cod, to continue with that example, accelerated in about 1979, due to increased severe coastal storms. What happens to a given floodplain will depend totally on local conditions. Many of our floodplains are not that often flooded, especially in glacial zones where they are filled up, and lower reaches of the giant rivers, and there is a lot of infrastructure in place that will initially control things.

Daniel Brouse:
You might be interested in King of Prussia and Plymouth Meeting, PA. The train derailment in Plymouth Meeting (July 17, 2023) was caused by extreme rainfall and flash flooding that resulted in sinkholes developing in the carbonate rock under the railroad tracks. In July and December of 2023, extreme rainfall resulted in sinkholes being exposed in the carbonate rock under Route 202 in King of Prussia, PA. I guess this is part of the local substrate conditions that vary widely from location to location.