why have streams failed to reduce their drainage basins to sea level?
338480
That is a good & interesting question.\n\nIn all logical aspects, this should occur due to the fact that everything in nature trys to balance out. This includes things like air pressure; it travels from high to low areas of pressure. In the same manner, everything that is uphill or of higher elevation trys to balance w/ those that are of lower elevation; hence erosion & drainage basins in general.\n\nIn order for this to occur, a lot of sediment would have to be washed into the drainage basin's streams & rivers. That would take a very long time.\n\nAlthough I think the answer here has to do with the fact that the earth's crust rebounds in a process called isostatic adjustment.\n\nWhen material is removed from the crust to another location, weight is taken off of an area. The crust will readjust to the former height by rising slightly.\n\nIt's just like placing several blocks of wood in a container of water. As you take off one of the blocks, the rest of them will rise in response to the reduced load.\n\nThats my answer & I'm sticking to it.\n\n:)
144386
Because in some cases there were no natural physical features like rivers or mountain ranges when the boundaries were determined.  Usually boundaries run along such features.
837311
Dams and levees change the course of rivers.  Farmig, forestry, and suburban development lead to erosion.  Mining can change the forms of mountains.
901727
If you're referring to a reverse flow due to natural OR artificial causes, the most noteworthy is the North fork of the South Branch of the Chicago River. This was reversed to have sewage flow down the Great Lakes/Mississippi waterway. The North Branch and South Fork of the South Branch were unaffected.\n\nSpeaking only of natural phenomena, there would, I am sure, be many. One I know of for sure is the Mekong, which is so close to sea level that the twice daily tides cause it to reverse flow and actually flow backward in some areas.
158282
Don't think there is one ... there is no major landmass interfering with the levels like there is between the Pacific and the Atlantic
258485
As water flows down rivers into the ocean, minerals dissolve in it. When the water gets to the ocean, solar radiation vaporizes the water and leaves the dissolved minerals behind. Over time, millions and millions of years, the concentration of these minerals increases.  The Salton Sea in California is an example of a speeded up version of the process. About the year 1909, the Colorado River was diverted from its course and flowed into the Salton Sea, which was a dry low area. It took some time to block the diversion. By the time it was complete there was a new fresh water lake there.  During the last 90+ years, that fresh water lake has turned into a sea more saline than the ocean.
65202
It's called a river delta. For example, the Mississippi Delta, the Nile Delta, etc. You could also be referring to a river channel mouth bar, which is only a small part of a delta found where the water speed slows from the opening up of the channel into the open ocean, thus causing the water to drop its sediment load.
593145
Deltas are not so much dependent on overflow of a river as they are on the amount of sediment a river is carrying & the velocity of the river.\n\nDeltas form from sediments "dropping out" of a river.\n\nDropping out refers to the sand, silt, and clay becoming to heavy for the river to carry.\n\nA river's carrying capacity (how much sediment it can carry at one time) is determined by how fast it is moving. The velocity is determined by how wide the channel is & how much water is running through it at one time.\n\nWhen a river nears the ocean it begins to slow down due to gravity and nearer the ocean, tidal interference. It's carrying capacity is lowered greatly.\n\nThe heaviest of the sediments begin to drop out first. This would be sand. The next would be silt. By the time it reaches the brackish water near the ocean, the clay will become too heavy due to interaction w/ the salt water. It too will "drop out".\n\nOver time, layers of sediment are built up. Eventually they will reach and exceed the water level of the river. This is the beginning of a delta.\n\nDeltas only form in river dominated areas. This means the areas where the amount of water & sediment from a river greatly outweigh the "strength" of the tides. Deltas will not form in areas where tides are strong. The sediment would be washed away by the action of the tides.
813560
Eons ago there were rivers\n\nTh
128765
We had a teacher at school who did a project on erosion that I still remember, so it must have taught us somehting.\n\nHe got a wheelbarrow load of fine sand and piled it into a mound out in theplayground. Then he got a hose and wet the top of it and let some of it wash away. \n\nNot only do you see a practical demonstration of the way that rain erodes mountains and forms streams and rivers but by varying the steepness of the mound or the speed of the water falling on it you can form shallow, broad wandering 'rivers' or steep sided straight valleys and so on.\n\nWe all thought it was prety cool that you could actualy see the rivers form as you watched.
919632
Dear Sir:\n\nYes, you have all the facts correct in your mind...\n\nWhat I see that you haven't got a good grip on is the \nsize of the problem.\n\nThe glaciers that the scientists are talking about extend for hundreds and hundreds of miles, and they are solid ice. They are presently sitting on solid ground and moving towards the water in a slow march, maybe 5 feet per day. These huge masses of ice are hundreds of feet high. So, the water they contain is just a massive amount of liquid when it melts. The terms gallons or liters is not applied to liquid in that huge of a mass. Terms like cubic miles is probably more appropriate. So when you talk about adding 2,000,000 cubic miles of water to the seas, some real changes in water level will probably result.\n\nIn the USA, a lot of homes and businesses are located at places where the elevation above the current sea level marks are only 1 to 3 feet.  High winds or storm surges could endanger places even higher up than that. In the area around New Orleans, La., the city is actually below sea level and is dry only because of a huge system of dikes that actually failed in a recent hurricane. As a result the city of New Orleans and much of the surrounding towns went under water.  Rebuilding, Clean-up, and repopulation could only begin after the waters receeded to their normal levels and the dikes were repaired, pumps placed back into service to clear out water behind the dikes, etc. \n\nWhat the scientists are suggesting is that in the future these flood waters might not receed...they will just stay there, and the flooded areas will stay flooded from now on...WOW.  That is a doozie to think about.
254827
Their legs have been modified into flippers so they would be unable to move an land.  Also their pelvic and pectoral girdles would not be able to support their weight with out the help of the water.
1049131
What i found on wikipedia- Reasons\n\nerosion by rivers, glaciers, or ocean waves create oversteepened slopes \nrock and soil slopes are weakened through saturation by snowmelt or heavy rains \nearthquakes create stresses that make weak slopes fail (see liquefaction, Hope Slide) \nvolcanic eruptions produce loose ash deposits, heavy rain, and debris flows. \nvibrations from machinery, traffic, blasting, and even thunder may trigger failure of weak slopes \nexcess weight from accumulation of rain or snow, stockpiling of rock or ore, from waste piles, or from man-made structures may stress weak slopes to failure and other structures \ngroundwater pressure acting to destabilise the slope \nin shallow soils, the removal of deep-rooted vegetation that binds the colluvium to bedrock.
233535
i always thought it was because there was no humidity in the air...probably wrong, anyway. or maybe its because the warm climate doesnt allow the moisture to turn back into water. who knows? prob a weatherman.
1115538
Well, there are actually a number of answers to that question. \n1) There are underground springs and water tables, which are why people had wells, and some folks still do today. Most western states have wells that reach into actual rivers that run beneath the surface, approx. 180 feet down. There are also windmills that pump water from underground springs and such.\n2) The polar caps are also almost 85% fresh water, and as they are slowly melting they are even now effecting the tides and current flows. Due to the changing salinity in the oceans, the Gulf Stream for one is already altering its course slightly..\n3) As the water began to lower, it was also evaporating, enriching the atmosphere with an increase of moisture. Thus, making the upper levels of the atmosphere richer, and raising the oxygen levels. Believe it or not, water has a direct impact on the air supplies.. Not many people realize that, but it's true.\n    Good luck with all your answers...
537660
The vertical rise must not exceed the head of water, or the riser will not work.
653800
Because when the storm forms, it forms from water that has evaporated from salt water. And the salt doesn't evaporate with the water.