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Please explain this logic. I'm not being facetious, but if that's just what happens over thousands or millions of years, why is there any coastline left at all

by axaxs 6y ago

Please explain this logic. I'm not being facetious, but if that's just what happens over thousands or millions of years, why is there any coastline left at all?

geographaway 6y ago
Plate tectonics. It's a broad area of study, but tl;dr, the planet's landmasses move and rise/fall independently of above-ground forces like erosion.
giardini 6y ago
b/c new land is constantly being created by the clash of the tectonic plates and by upwelling of volcanic activity. Once all geological activity ceases (several billions of years in the future) then land might eventually erode away and the Earth's surface might briefly be covered completely with water. However, eventually all water will escape the planet's gravitational field and Earth will become, like Mars, a dead planet. See "Here's What'll Happen When Plate Tectonics Grinds to a Halt": https://www.nationalgeographic.com/science/2018/08/news-happens-plate-tectonics-end-earth-mountains-volcanoes-geology/ https://www.nationalgeographic.com/science/2018/08/news-happ...
rckoepke 6y ago
You brought up Daytona. Florida's an interesting case where discussions of plate tectonics may be off the mark. Seems like it was formed mainly by deposition of seashells, shellfish, corals and sand and clay over the past 30 million years.[0] Looks like water levels were higher over most of that time period (p.71), so sea life could exist there and steadily build up a mineral base over time. It's also been much lower recently. Over the past 18,000 years sea level has risen 120m[1]. p. 71 in that book shows more detail for sea level over the past 5 million years than the wikipedia link. Here are some color renderings of what florida probably looked like from LEO over the past 40 million years[2] It seems that in places where magma is not pushing up new continental landmass (e.g. Florida), new land is created by sedimentation only underwater, while water levels are high. Then it's exposed when water levels recede, but when water levels rise again, that land is eroded and reclaimed until it is completely underwater, at which point it may grow again if there is an abundance of shellfish and coral. Right now we seem to be at the "rising sealevel, quickly-eroding shoreline" part of the cycle, which is inconvenient for human development. 0: http://gen.lib.rus.ec/search.php?req=The+Geology+of+the+Everglades+and+Adjacent+Areas http://gen.lib.rus.ec/search.php?req=The+Geology+of+the+Ever... 1: https://en.wikipedia.org/wiki/Past_sea_level https://en.wikipedia.org/wiki/Past_sea_level 2: https://www.nps.gov/common/uploads/teachers/lessonplans/Material_1_Florida-paleo-geography-maps-4.pdf https://www.nps.gov/common/uploads/teachers/lessonplans/Mate...
refurb 6y ago
The coastline is constantly shifting. Growing in some parts, eroding in others. Interestingly, Sandwich, UK used to be a major port with a navigable waterway to the North Sea. It's now 3km inland.[1] [1]https://en.wikipedia.org/wiki/Sandwich,_Kent https://en.wikipedia.org/wiki/Sandwich,_Kent

by axaxs 6y ago

Please explain this logic. I'm not being facetious, but if that's just what happens over thousands or millions of years, why is there any coastline left at all?

geographaway 6y ago

Plate tectonics. It's a broad area of study, but tl;dr, the planet's landmasses move and rise/fall independently of above-ground forces like erosion.

giardini 6y ago

b/c new land is constantly being created by the clash of the tectonic plates and by upwelling of volcanic activity. Once all geological activity ceases (several billions of years in the future) then land might eventually erode away and the Earth's surface might briefly be covered completely with water. However, eventually all water will escape the planet's gravitational field and Earth will become, like Mars, a dead planet. See "Here's What'll Happen When Plate Tectonics Grinds to a Halt": https://www.nationalgeographic.com/science/2018/08/news-happens-plate-tectonics-end-earth-mountains-volcanoes-geology/ https://www.nationalgeographic.com/science/2018/08/news-happ...

rckoepke 6y ago

You brought up Daytona. Florida's an interesting case where discussions of plate tectonics may be off the mark. Seems like it was formed mainly by deposition of seashells, shellfish, corals and sand and clay over the past 30 million years.[0] Looks like water levels were higher over most of that time period (p.71), so sea life could exist there and steadily build up a mineral base over time. It's also been much lower recently. Over the past 18,000 years sea level has risen 120m[1]. p. 71 in that book shows more detail for sea level over the past 5 million years than the wikipedia link. Here are some color renderings of what florida probably looked like from LEO over the past 40 million years[2] It seems that in places where magma is not pushing up new continental landmass (e.g. Florida), new land is created by sedimentation only underwater, while water levels are high. Then it's exposed when water levels recede, but when water levels rise again, that land is eroded and reclaimed until it is completely underwater, at which point it may grow again if there is an abundance of shellfish and coral. Right now we seem to be at the "rising sealevel, quickly-eroding shoreline" part of the cycle, which is inconvenient for human development. 0: http://gen.lib.rus.ec/search.php?req=The+Geology+of+the+Everglades+and+Adjacent+Areas http://gen.lib.rus.ec/search.php?req=The+Geology+of+the+Ever... 1: https://en.wikipedia.org/wiki/Past_sea_level https://en.wikipedia.org/wiki/Past_sea_level 2: https://www.nps.gov/common/uploads/teachers/lessonplans/Material_1_Florida-paleo-geography-maps-4.pdf https://www.nps.gov/common/uploads/teachers/lessonplans/Mate...

refurb 6y ago

The coastline is constantly shifting. Growing in some parts, eroding in others. Interestingly, Sandwich, UK used to be a major port with a navigable waterway to the North Sea. It's now 3km inland.[1] [1]https://en.wikipedia.org/wiki/Sandwich,_Kent https://en.wikipedia.org/wiki/Sandwich,_Kent