Margin Call Level is the margin level at which you are in danger of having some of your positions forcibly closed (or "liquidated"). If this happens, your positions will be closed in the order they were created, first to last. The margin call level can vary depending on the volatility of the currency pair, but a rough estimate is 80%. The exact levels for each currency pair are listed under Fees and Pair Info (in the "Help" section).
The number of positions closed is at our discretion - we may close all your positions or only enough to get your margin level above 100%. Positions are liquidated to increase the chances that you can repay the funds you have borrowed using the value of your positions and account balance and protect our reserves for leveraged trading.
Margin Call Level notifications are sent by email, but are not always guaranteed. As such, it is important to proactively monitor your margin level.
Margin Liquidation Level is the margin level at which all your positions are automatically liquidated. This level can vary depending on volatility, but a rough estimate is about 40%. The exact levels for each currency pair are listed under Fees and Pair Info (in the "Help" section).
At the Margin Call Level and below, liquidation is at Kraken's discretion. That means that liquidation can happen at any point between the margin call level of 80% and the Margin Liquidation Level.
Note that once the liquidation process has started, it is not possible to stop it. The process is automated and our customer support team has no ability to stop liquidations once they have started.