Teach me Geography

[AdmundfortGeographer]

How would an area of desert (if on an island) meet the coastline?

That depends. What's the topography and terrain? How large an island?

 

[ender_wiggin]

Warm. Sandy. Total island size probably about 600 miles from one end to the other, the area of desert, however, is probably only 100-150 miles from coast to coast.

 

[Catavarie]

Thanks.

How would an area of desert (if on an island) meet the coastline?

Well Salt water is not the best for sustaining plant life on land. Need a Botonist to explain this fullly, but it has something to do with the chemical differences than with fresh water.

 

[AdmundfortGeographer]

Well Salt water is not the best for sustaining plant life on land. Need a Botonist to explain this fullly, but it has something to do with the chemical differences than with fresh water.

About the only way vegetation on land is supported by sea water is in mangroves. Basically swamps that are influenced by tides. You can have these by desert terrain, but they are usually close to where a river is spilling into the sea. However, mangrove swamps are swamps. Meaning they are pretty much flooded forests. You could have a rivers coming down from the high topography of the two large sides into the low, sandy ithsmus. But the rivers wind through sandy wastes until they spill into the sea where they feed a mangrove swamp.

Somalia is a perfect example of this, basically a flat desert throughout, but the sparse rivers through the country feed a few significant mangrove forests near the coast.

 

[ender_wiggin]

So you'd have one big ass mangrove maintaining the border between the entire desert and the ocean, or do mangroves specifically need both fresh water and salt water sources (the former being your said river)?

If the latter is true, what other terrain constitutes the border between sea and desert.

Do deserts ever just become beaches?

 

[AdmundfortGeographer]

Do deserts ever just become beaches?

Of course they do. Where there isn't a river dumping into the sea. Which is all over the place of course.

"Significant" doesn't have to mean "one big ass" blank. And a mangrove is a flooded forest at sea level. Jump above sea level a little and it can't exist. Drop the ground too deep from the surface and no trees can take root. Remove the source of fresh water, and there is no land vegetation.

It's all up to you how suddenly the sea drops off where the coastline is. It's up to you how steep the sandy shore it. It's up to you where water that feeds rivers drains off high topography, send it where ever you want.

 

[TheAuldGrump]

Imagine, "Your fight with the crocodiles has disturbed the hippos. Their stampeding over you wakens the dragon turtle and alerts the sphynx."

Of them the hippo is likely the most dangerous... They may look funny, but them things is mean!

The Auld Grump, not joking at all...

 

[Meloncov]

In regards to the desert/mountain forest, yes it is entirely possible. Presumably, you know that as water vapor cools it condences, and that higher elevations give lower tempertures. As damp air is blown into a mountain, it is forced upwords and cools. This causes condensation, and thus rain. Once it has passed over the mountain, much of the moisture has been lost, and it is unlikely for much rain to fall on the other side. This leads to one side of the mountain to be relatively damp, while the other is quite dry, as happens in my hometown of Albuquerque (alas, we are on the dry side).

Inorder for this to happen, the mountians need to be between the desert and the nearest major source of moisture (genearally a ocean or sea).

 

[mythusmage]

A Rough Guide to Deserts

Deserts come about for three reasons; latitude, blocking, distance. The Sahara in North Africa came about because of wind patterns. Moisture laden air stopped reaching North Africa soon after the end of the last Ice Age and things dried out. The Mojave on the other hand is a desert thanks to mountains. Back when the continents were clumped together into Pangaea the center of the supercontinent was a desert because it was real far from the ocean.

Coastal deserts are possible when said coast lies next to a cold water current, and humid air is kept away. The Nazca in South America and the Skeleton Coast in Africa are examples of this. In the case of the former humid air from the east is blocked by the Andes, in the case of the latter the Skeleton Coast lies at the right latitude. The cold water currents help to make the situation worse. The Galapagos are another example of a cold water current combining with latitude to produce desert terrain.

Where high altitude forests lying next to low altitude desert are concerned, Southern California is a lousy example. Taken as a whole the average rainfall is low enough to qualify the area as a desert. Trouble is, Southern California is not homogonous in terms of terrain and climate. A better example would be the state of New Mexico. The New Mexico desert has mesas scattered throughout and is bordered by low mountains. The high ground gets more rain and as a result can support forests.

Then you have an altitude related phenomenon known as "virga". Virga is rain that doesn't reach the ground. Around here (San Diego CA) virga tends to evaporate before it gets below 5,000 feet.

What this all means is that yes, you can have an island with forested mountains at either end and an arid lowland inbetween. All you need are mountains high enough to catch the rain that would otherwise evaporate before hitting the ground.

There are additional complications, but this should cover the basics.

 

[S'mon]

Alright, I have enough common sense and introductory biology to make the obvious guesses, but I want to bounce these questions off of someone who knows what they're talking about.

In a hot climate, how does elevation change biome?
--- > Can a forest exist on the mountains when the nearby lowlands are desert?

Definitely - if you go to New Mexico you'll see the high mountains are covered in forest whereas the rest of the state is high-altitude desert plateau. The mountains force hot desert air upwards, it cools and rain falls on the mountains.

Edit: As pointed out by Meloncov above.