You can use jquery .scroll method for achieving this. You can show the code to show the menu in the .scoll event handler
<!DOCTYPE html>
<html>
<head>
<style>
div { color:blue; }
p { color:green; }
span { color:red; display:none; }
</style>
<script src="http://code.jquery.com/jquery-latest.js"></script>
</head>
<body>
<div>Try scrolling the iframe.</div>
<p>Paragraph - <span>Scroll happened!</span></p>
<script>
$("p").clone().appendTo(document.body);
$("p").clone().appendTo(document.body);
$("p").clone().appendTo(document.body);
$(window).scroll(function () {
$("span").css("display", "inline").fadeOut("slow");
});
</script>
</body>
</html>
You can find the documentation and sample here