This is not true, the mempool only removes txs that have been included in the block. Why would it just drop the rest of the not yet confirmed transactions?
There is no threshold set by the miners. One can choose any tx fee he/she wants (you can even have a tx with no fee, but don’t expect it to get confirmed). But if the mempool is full one might have to wait a long time for its tx to get mined. 
1.A mempool is a list of unconfirmed transactions that make sense to a particular node.
2.The mempool gets bigger, transactions take longer to go into the block ,transaction fees are getting higher.
3.If a mempool is growing the transaction fees are too.
#1mempool is side by side with its own node a miner will check for the highest fees using the mempool system a miner is a node so it can check its own mempool
#2mempool builds bigger and bigger
#3the miner will go after the highest fees to build new block so pay more be first to enter blockchain
Homework on Mempool - Questions
What is the mempool?
When someones wallet makes a transaction, the information of that transaction is then sent out successively to all other nodes on the Bitcoin network. It’s only a matter of time before the information has reached all nodes. When the information of the new transaction reach a node it’s added to that nodes pool of unconfirmed transactions, if it makes sense to the node in light of its copy of the blockchain. A transaction is unconfirmed until a miner includes it in the formation of a new block on the blockchain. A nodes pool of unconfirmed transactions is called the mempool.
What happens if the miners can’t keep up with the rate of the new transaction?
The mempool then grows on the network as a whole. The users of the blockchain experience longer transaction times.
How does a growing mempool effect transaction fees?
In theory it doesn’t have to affect the fees, since there’s no obvious connection. But if users are suffering from longer transaction time and want to circumvent the growing body of transactions waiting to be included in the next block, then they can choose to pay a larger fee in order to be prioritized by the miners. In that case the fees in general will go up.
What is the mempool?
The mempool is a collection of unconfirmed transactions
What happens if the miners can’t keep up with the rate of the new transaction?
The size of the mempool will grow.
How does a growing mempool effect transaction fees?
A bigger mempool size means more transactions are waiting for confirmation. It will take longer for a transaction too be confirmed. Transactions with a higher fee go first so fees will rise.
A Mempool is a list of unconfirmed transactions.
If Miners cannot keep up with transactions the mempool will grow and Miners will process the one with the highest fee write it into the block first, and put as many as possible in the next block.
3.a growing mempool will most likely create compitition and raise the fees.
1 - mempool is the buffer were the unconfirmed transactions wait to be added to blockchain.
2 - The transaction start to be slower over time.
3 - when the mempool is too big the user in order to get prioritize increases the fee to pay to the miner, in that way his transaction is more susceptible to be added to the blockchain first.
What is the mempool?
A mempool is a list of all unconfirmed transactions. When a transaction is initiated by a wallet, it is broadcast to the network. Nodes pick it up, ascertain it meets protocol requirements and transmit it onward. Each node that accepts this transaction then adds it to its mempool list. At any point, mempool lists may differ on each node, but over time they tend to align.
What happens if the miners can’t keep up with the rate of the new transaction?
Unconfirmed transactions will stay in the mempool till they are picked up by miners for the next block. The mempool list grows larger and transaction time on the network increases
How does a growing mempool effect transaction fees?
As the mempool grows, transaction fees tend to increase as transactors offer to pay higher transaction fees to get miners to prioritize their transactions.
Mempool is like a waiting area, this is a pool of unconfirmed transactions that are waiting to be confirmed by the miners, before they will be added on the block.
The mempool will grow and there will be delayed in most of the transactions that are stuck in the mempool, before they will be added on the blockchain, this means longer transaction times.
Transaction fees will soar high since mempool is getting larger and larger it means miners will also demand for higher and higher fees for them to verify those large number of transactions that are stuck on the mempool, and as always the higher the fee a transaction pays, the more it will be prioritized to be handled first.
What is the mempool?
Transactions are sent to the mempool in order to be confirmed , it is like a waiting area for ttranactions to be confirmed
What happens if the miners can’t keep up with the rate of the new transaction?
I think it stays in the mempool until it becomes more attractive to the miners , eventually it can fail and not go through .Miners look at the TX with the most satoshis per byte to make money so in busier times only the most profitable transactions with be confirmed relatively quickly . I once had a trade fail because my transaction was stuck in the mempool . I had forgotten to change the fee.
How does a growing mempool effect transaction fees?
They will increase as people want their transaction to go through straight away
The mempool is a list of unconfirmed transactions. Each node in the network has its own list of unconfirmed transactions. Because it takes time for nodes to propagate these unconfirmed transactions across the network, the mempool of each node is not necessarily identical, but over time each node will eventually pick up these transactions.
If miners can’t keep up with the rate of new unconfirmed transactions, the mempool will grow.
In our traditional financial system, fees usually consist of a flat amount + a flat rate e.g. $2 + 1% for an international transaction. In the blockchain, fees are determined in Satoshis per Byte (Sat/B), where 1 Satoshi = 10^(-8) BTC. This is because transactions which are larger in size - size here referring to ‘bytes’ - take up more block space, so miners cannot fit as many transactions onto a single block. So the more complicated a transaction (e.g. multiple inputs and multiple outputs), the higher the fees. However, this means that if high volume transactions (e.g. 1 MIL BTC) can be constructed in a way such that they only take up a small amount of bytes, then you can get very small fees (e.g. 0.1 BTC, following the previous example) despite the high volume transaction. This usually takes a longer time to find such construction, so the time to process the transaction will be longer. Moreover the larger the mempool, the larger the competition in terms of getting your transaction processed first. Users who want their transactions processed first can then pay higher fees, in a way negating the need for miners to find constructions that take up less space on their blocks. Higher fees also attracts more miners, bumping up the transaction in miners’ lists of transaction priorities.
A list of blockchain transaction that need to be computed.
The backlog grows.
We increase fees to entice miners.